Internet reports that the U.S. and British governments have asked citizens in Qatar to keep a low profile after Iran vowed to retaliate for a U.S. attack on its nuclear facilities. "Out of caution, we recommend that U.S. citizens remain in place and take refuge until further notice," the U.S. Embassy in Doha said in a statement on Monday. British Foreign Secretary Lamy also made a similar statement in Parliament. On Monday, Iran's military chief said Iran's response to the weekend attack in Washington would be "proportionate." It is reported that Qatar has the largest U.S. base in the region. The base is called Al Udeid and is also the U.S. Central Command's command headquarters in the Middle East. It oversees U.S. military operations in the Middle East. In Qatar, there are currently approximately 9000 U.S. military personnel. Qatar's Ministry of Foreign Affairs recently announced that Qatar will temporarily close its airspace to ensure the safety of tourists and residents.