In May 2019, four merchant ships were attacked by limpet mines in the Gulf of Oman. Tensions rose between the United States and the Islamic Republic of Iran, after the United States blamed Iran's Islamic Revolutionary Guard Corps for the incident. In June 2019, a nearly-identical incident occurred involving two merchant ships. In December 2019, the United States began discussing with Iraq about plans to withdraw from certain bases. That same month, the K-1 Air Base was attacked, resulting in one American fatality and six injuries. The United States claimed that Kata'ib Hezbollah, an Iranian proxy group, was responsible for the attack. The United States responded by conducting airstrikes in Iraq and Syria against Kata'ib Hezbollah locations.