The US Department of Justice says it wants to interview senior figures involved with the BAE Systems and Saudi Arabia arms contract as part of its corruption investigation.
The US investigation could lead to requests to interview those involved with signing the original £43m contract in 1985, including former Prime Minister Baroness Thatcher, UK newspaper The Times reports.
The Al-Yamamah contract has come under intense scrutiny amidst allegations of corruption. It is alleged the British Government paid Saudi Prince Bandar bin Sultan more than £1bn through BAE.
However, investigators could have difficulty accessing the information it wants, as much of it is protected by the Official Secrets Act.
A UK Serious Fraud Office investigation into the contract was abandoned last year at the request of the government, which said it would jeopardise national security.