The US and UK governments have asked their citizens in Qatar to keep a low profile after Iran vowed to retaliate against US attacks on its nuclear facilities. "Out of an abundance of caution, we advise US citizens to remain in place and take refuge until further notice," the US embassy in Doha said in a statement on Monday. British Foreign Secretary Lamy also made a similar statement in parliament. On Monday, the head of Iran's military said Iran's response to Washington's weekend attack would be "proportionate". It is reported that Qatar has the largest US base in the region. The base, called Al Udeid Air Base, is also the command headquarters of the US Central Command in the Middle East, which is responsible for overseeing US military operations in the Middle East. In Qatar, there are currently about 9,000 US troops. Qatar's foreign ministry recently announced that Qatar has temporarily closed its airspace to ensure the safety of tourists and residents.