The United States of America are planning to send around 1,000 security officers to protect their athletes at the London Olympics next year.
Half of that number are expected to be FBI agents, charged with the task of ensuring that the country's diplomats are safe.
The US are said to be particularly worried about the adequacy of the United Kingdom's anti-terrorism plans.
It has also been reported that American officials have sought a breakdown of the number of British police and other security personnel that will be available at the Games.