The Government has insisted it has "full confidence" in its security plans for next year's Olympics, after reports the US is worried about protection levels.
According to the Guardian, the US is preparing to send up to 1,000 of its own agents, including 500 from the FBI, to look after America's contestants and diplomats at the event.
The newspaper reported that US officials have raised "repeated concerns" about security. The restriction of the scope of anti-terrorism stop-and-search powers is claimed to be one of their reasons for concern.
Earlier this year, National Olympic security co-ordinator Chris Allison, of the Metropolitan Police, said he believes 12,000 officers will be needed nationally to police the event. Another 10,000 to 15,000 security officials could also be deployed by firm G4S.
The Ministry of Defence is also understood to be involved in security discussions.
A Home Office spokesman said: "Security planning is on track and funding has been protected. The Government is committed to delivering a safe and secure Games that London, the UK and the world can enjoy.
"The International Olympic Committee (IOC) undertake detailed inspections of security preparations and have full confidence in our plans. The UK has a strong and close working relationship with the US, who have expressed similar confidence.
"The Government, London 2012 Organising Committee (LOCOG) and G4S are working together to finalise the requirement for venue security and as is common at major events in the UK we will make the best and most appropriate use of all available resources."
A Home Office source said it does "not recognise as true" the suggestions that there are concerns from the US.
The US state department declined to comment, and the FBI was not available for comment.