Several merchant ships in the Persian Gulf were damaged in two incidents in May and June 2019. Western nations blamed Iran, while Iran denied involvement. In June 2019, Iran shot down an American RQ-4A surveillance drone flying over the Strait of Hormuz, sharply increasing tensions and nearly resulting in an armed confrontation. In July 2019, an Iranian oil tanker was seized by Britain in the Strait of Gibraltar on the grounds that it was shipping oil to Syria in violation of European Union sanctions. Iran later captured a British oil tanker and its crew members in the Persian Gulf. Both Iran and the UK later released the ships. Meanwhile, the U.S. created the International Maritime Security Construct (IMSC), which sought to increase "overall surveillance and security in key waterways in the Middle East", according to the United States Department of Defense.