US embassy officials are considering a move from their current address as part of a wholesale security review.
The US embassy has been in the square since the 18th Century
Washington has undertaken a global sell-off of government buildings after bringing in strict new safety measures.
An embassy spokesman said officials were "pursuing alternatives... to provide a modern secure facility for this important mission".
The building in Grosvenor Square, central London, has been home to the the US embassy since the 1960s.
"We are looking at potentially viable sites that could be acquired for new construction but that's just one option," the spokesman said.
He said one of the alternatives was to remain in place and upgrade the facilities.
The 133,300 sq ft property has 939 years left on the 999-year lease.
The US has had an embassy in Grosvenor Square since the late 18th Century.
General Dwight Eisenhower is said to have worked there in the 1940s while planning the invasion of North Africa in World War II.
Any new premises would have to meet strict safety requirements brought in after the 1998 bombings of the US embassies in Kenya and Tanzania, and tightened after the attacks on the US on 11 September 2001.
Those that do not, or cannot be upgraded, with the exception of about 150 "culturally significant" properties and others given special waivers, must be abandoned by US diplomats.
The embassy's Navy Annexe, the US Navy's former UK offices, is also in the square, and was recently put on the market for more than £100m.