The US has offered to send an aircraft carrier to be stationed off the British coast and boost security during the 2012 London Olympics, reports said on Sunday.
The offer, however, has reportedly been rejected by London because it would make Britain look "weak", the Daily Mail reported.
Downing Street has not said anything on the report. But sources told the paper the ministry had been offered a US carrier, based in the Thames estuary, to help defend the skies over London and eavesdrop on any terrorist activity.
The US offered a 40,000-tonne Wasp class amphibious assault ship, which carries up to 40 Sea Knight helicopters for ferrying of marines and equipment, as well as up to 20 Harrier II attack aircraft. It also boasts of a battery of missiles capable of shooting down planes in the event of an attempt to copy the 9/11 attack.
The report said the "main motivation" for the offer was America's self-interest. If the Olympics were the object of a terrorist attack, US forces could launch operations from the ship to airlift American citizens to safety.
In the past, the Olympics have been a target for terrorists. In 1972, Israeli athletes were killed at the Munich games.
A ministry spokesman has said plans were being drawn up for a naval vessel to offer aerial defence in the Thames estuary during the games, but it was likely to be a British ship.
"We haven't made final decisions yet. There are a lot of options available, including Special Forces. But we are certainly capable of protecting ourselves. The Royal Navy can provide a Type 45 destroyer for aerial defence."
The US Navy had sent a frigate to patrol the Greek coast during the 2004 Athens Olympics. But Greece had admitted it needed help with security.