Since September 2013, China has undertaken extensive land reclamation and construction on several reefs in the Spratly island chain in the southern part of the South China Sea, raising a variety of concerns in the United States and Asia. Photographs released by sources including IHS-Jane's, the Center for Strategic and International Studies (CSIS), and China's Xinhua News Agency show large-scale reclamation that has increased the size of some land features by several times and created completely new land features that had previously been submerged reefs. China's Foreign Ministry announced on June 16, 2015, that China would complete its reclamation work "in the upcoming days" and then turn its attention to building facilities on the newly created artificial islands. Each of the areas under reclamation—including Cuarteron Reef, Fiery Cross Reef, Gaven Reef, Hughes Reef, Johnson South Reef, Mischief Reef, and Subi Reef (see table and map, below)—is disputed between China and at least one other claimant, including the Philippines, Vietnam, Malaysia, and Taiwan. At least three—Hughes Reef, Johnson South Reef, and Mischief Reef—are within the 200-nautical mile exclusive economic zone (EEZ) that the Philippines claims from its nearest primary landmass, the island of Palawan. In a May 30, 2015, speech, Secretary of Defense Ashton Carter said China had created over 2,000 acres (809 hectares) of land in the South China Sea in the past 18 months, "more than all other claimants combined ... and more than in the entire history of the region." China has also undertaken construction of harbors, radar towers, an airstrip long enough to support most military aircraft, and other facilities. Defense Department officials have also reportedly identified artillery vehicles on at least one of the artificial islands. The reclamation activity continues a series of assertive actions by China in the South China Sea as Beijing seeks to more actively stress its sovereignty claims in the area. These actions have led the U.S. government to argue that China is seeking to strengthen its maritime territorial claims using threats, coercion, and other actions that fall short of direct conflict. U.S. officials point to Chinese actions including more extensive patrols by Chinese maritime authorities and other Chinese vessels, the blockading of some disputed features by Chinese maritime authorities, the announcement of fishing bans, energy exploration in disputed waters, and now the reclamation and infrastructure improvements on several Chinese-controlled features. In the view of many experts, these actions have substantially heightened regional tensions and raised the potential of military conflict in some of the world's most heavily trafficked waters, through which around $5 trillion in ship-borne commerce passes each year. China argues that it holds sovereignty over each of the features and therefore is acting legally. It points out that other claimants, including Vietnam, the Philippines, Malaysia and Taiwan, have also reclaimed land and fortified features in the area; that one claimant, Vietnam, occupies considerably more features in the Spratlys than China does; and that others have constructed airstrips and based troops on features they control. Other observers, including U.S. government officials, argue that the scale of China's current reclamation dwarfs that by any other actor in the South China Sea and is inconsistent with the (non-binding) 2002 Declaration on the Conduct of Parties in the South China Sea (DOC). In March 2015, U.S. Pacific Fleet Commander Harry Harris, Jr., stated that, "the scope and pace of building man-made islands raises serious questions about Chinese intentions." In the May 30, 2015, speech, Secretary of Defense Carter said, "... with its actions in the South China Sea, China is out of step with both the international rules and norms that underscore the Asia-Pacific's security architecture, and the regional consensus that favors diplomacy and opposes coercion." China's land reclamation in the South China Sea raises a number of questions for the United States. Among them: Is the reclamation activity legal? What are its implications for China's ability to make arguments about its sovereignty and maritime rights in the area? What are China's motivations for pursuing reclamation activity now? Does the reclamation activity improve China's ability to operate military and other assets further from the Chinese coast, and what would this ability allow the People's Liberation Army (PLA) and other Chinese institutions to do? Does the reclamation threaten or affect U.S. interests including freedom of navigation and freedom of the high seas? Does the reclamation substantially change the status of diplomatic efforts to reduce tensions and resolve sovereignty disputes in the region? How does Chinese reclamation activity affect U.S. strategy in the region? What are the appropriate responses for the United States? CRS consulted with U.S. government and outside experts on the legal, military/operational, diplomatic, and economic implications of China's activities. Among CRS's findings are the following. Although others, including Vietnam, Malaysia, the Philippines, and Taiwan, have also reclaimed and/or reinforced land features in the area, China's reclamation is by far the most extensive any nation has undertaken on disputed features in the South China Sea. It is difficult to judge the legality of the Chinese reclamation activity, given that sovereignty over the features affected is not settled. Reclamation, per se, is not illegal on features over which a nation has sovereignty. However, each of the features is claimed by at least two parties, so each is clearly disputed. Moreover, some features in their original form may not have extended above water at high tide, meaning no sovereignty claim to those features is recognized under the United Nations Convention on the Law of the Sea (UNCLOS). Under UNCLOS, the reclamation does not allow China to claim broader 200-nautical-mile EEZs around the reclaimed landmasses. The most that a nation could claim around any of the features is territorial waters extending 12 nautical miles from the feature, and this is only claimable if, before reclamation began, the reef included features above water at all times. So far China has not asserted new legal claims based on its artificial island building. China has so far confined its latest wave of reclamation and construction work to features it already occupied in the Spratly Island chain. It does not appear to have sought to carry out such work on features it did not previously control, including those occupied by other claimants. The reclamation arguably violates the spirit of the 2002 Declaration on the Conduct of Parties in the South China Sea (DOC) between China and the Association of Southeast Asian Nations (ASEAN) and makes discussions over a potential Code of Conduct more difficult. The reclamation includes areas under consideration in an ongoing UNCLOS arbitration case, in which the Philippines seeks a ruling on the legality of Chinese claims and behavior in the South China Sea. The Philippines has asked for a ruling on the legal status of each of the features under reclamation, among others. Such a ruling could clarify the rights of all parties in areas surrounding the features. The reclamation efforts could improve China's ability to maintain ship and aircraft operations in the region on a day-to-day basis, including patrols of disputed features in the South China Sea, and to conduct combat operations in the region. China could use one or more of the reclamation sites as locations for anti-access/area denial (A2/AD) systems, including radars, electronic listening equipment, surface-to-air missiles (SAMs), anti-ship cruise missiles (ASCMs), and manned and unmanned aircraft. China may be undertaking reclamation now in a way that it did not previously in part because of its development of more sophisticated dredging capabilities that make it easier for it to perform such work far from the Chinese mainland. One set of questions surrounding China's reclamation and construction activity is whether it can be considered legal, what additional rights China may seek to claim based on the features, and whether the activity in any way hinders the rights of other parties to navigate in the waters and airspace surrounding the features. International law, as embodied in UNCLOS, governs the rights of states with respect to maritime zones, which are defined in terms of proximity to a coastal state. China and other claimants, including Vietnam, the Philippines, Malaysia, and Brunei, are parties to UNCLOS, although under the terms of Beijing's accession it did not agree to many of the convention's dispute resolution mechanisms. The United States is not a party to the convention, but it has said it abides by most of the convention's terms for claiming maritime rights. With respect to maritime disputes, the United States has consistently stated that it takes no position on the specific sovereignty questions but urges the parties involved to resolve the disputes peacefully, according to international law, and to refrain from using coercion, force, or threat to strengthen their claims. UNCLOS recognizes that coastal states may claim maritime zones in which they may exercise certain rights: Territorial Sea : A coastal state is entitled to claim a belt of sea adjacent to its coast as its "territorial sea." This territorial sea may extend up to 12 nautical miles from the coast, and in this belt of sea the coastal state may exercise full sovereignty. (UNCLOS articles 2-3) Contiguous Zone : A coastal state may also establish a zone adjacent to its territorial sea as a "contiguous zone." Within this zone, the coastal state is not sovereign, but it may exercise the control necessary to prevent and punish infringements of the customs, fiscal, immigration, and sanitary laws and regulations that apply in its territorial sea. The contiguous zone may extend up to 24 nautical miles from the coast.