Relations between the U.S. and North Korea were contentious during the Obama administration, largely due to conflict over the North Korean nuclear weapons program and threats of military action. Not long after Obama took office North Korea elbowed its way back onto the international stage after a period of relative quiet, drawing accusations of planning a new long-range intercontinental ballistic missile test weeks after Obama was sworn in and performing an unannounced nuclear warhead and missile testing in late May 2009 to the disapproval of the State Department. Relations were further strained with the imprisonment of American journalists Euna Lee and Laura Ling for their alleged illegal entry into North Korean territory on assignment for a media organization. although both women were later released on August 5, 2009. Later that year, Pyongyang announced its intention to terminate the 1953 armistice ending hostilities in the Korean War on May 28, 2009 effectively restarting the nearly 60-year-old conflict, and prompting the South Korea-United States Combined Forces Command to Watchcon II, the second-highest alert level possible. In 2010, two more major incidents with North Korea occurred: the sinking of a South Korean Navy Ship that actuated new rounds of military exercises with South Korea as a direct military response to sinking and the Bombardment of Yeonpyeong prompting the US aircraft carrier to depart for joint exercises in the Yellow Sea with the Republic of Korea Navy, to deter further North Korean military action. In light of the geopolitical developments with North Korea, the Obama Administration had called the U.S.–South Korean alliance as a "cornerstone of US security in the Pacific Region." During Obama's presidency, North Korea's nuclear-weapons and missile program became "steadily more alarming" to the United States and Obama was criticized for failing to hinder or eliminate the program.