The United States removed the bombers that were stationed at an air base in the United Kingdom on Sunday after security concerns were reignited following an initial suspected terrorist plot, according to a U.S. official.

The Royal Air Force Fairford Base’s security was called into question last Sunday when five British nationals were arrested on suspicion of planning a terrorist attack near the air base, which has been used by the U.S. military to launch strikes throughout the conflict in Iran. British Prime Minister Andy Burnham said on Thursday “there are strong indications that Iran played a part” in the incident, which the White House initially presumed. The men were released on bail the following day, a decision that was quickly criticized by President Donald Trump.