By Andrew Mills

DOHA (Reuters) -Qatar said on Monday it had shut down its airspace temporarily, hours after U.S. and British authorities contacted their citizens there recommending that they shelter in place until further notice.

The U.S. and British announcements, which triggered a slew of messages from many Doha-based institutions to employees and students, came as Iran repeated earlier threats to retaliate against the U.S. after strikes on its nuclear sites.

Qatar hosts Al Udeid Air Base, the largest U.S. base in the Middle East, which serves as the forward headquarters for U.S. Central Command and accommodates approximately 10,000 troops.

Two U.S. officials separately told Reuters that Iran could carry out attacks targeting American forces in the Middle East soon, with one source saying it could happen in the next day or two.

The messages from Britain and the U.S. embassy in Qatar said their recommendations were made "out of an abundance of caution" and offered no further information.

Qatar's foreign minister said on X that its airspace would be closed as part of measures taken amid developments in the region, without going into further detail.

Earlier, Qatari foreign ministry spokesperson Majed Al Ansari had released a statement saying the security situation there remained stable.

Many Qatar residents were confused by what they said appeared to be mixed messaging from Qatari and U.S. embassy officials.

The Qatar campuses of American universities in Qatar sent messages to staff and students after the embassy announcement.

Texas A&M University said an evacuation of its building had been ordered, Northwestern University asked people to go home and Georgetown University said people could go home if they wished.

The American School, which is not in session, closed its campus and cancelled summer camps until further notice.

(Reporting by Andrew Mills and Tala Ramadan; writing by Maha El Dahan; Editing by Kevin Liffey, Aidan Lewis and Andrew Heavens)