BAE Systems is fighting back after last week being sacked by the US Army on a contract to supply military trucks.

The UK arms giant, which has made a big play of targeting the American armaments market, said today it has formally protested to the Government Accountability Office, a US body similar to Britain's National Audit Office.

The loss of the $281 million (£171.3 million) follow-on contract sent BAE's shares tumbling more than 5% last week.

BAE's protest letter states the US Army did not do its job properly when it awarded the additional Family of Medium Tactical Vehicles contract to rival US outfit Oshkosh Defense.

In a statement to the Stock Exchange, BAE said: “After a detailed analysis of the information provided by the US Army before and during the formal competition debrief, the company believes that the Army did not properly evaluate the proposals, consistent with the government's stated requirements and the Army failed accurately to assess the various risks associated with the different proposals.”

The contract to supply the trucks has been held since 1991 by Armor Holdings, the US defence contractor which BAE bought a couple of years ago for £2.3 billion.

More than 50,000 of the vehicles which transport troops and haul arms and hardware around combat zones like Afghanistan and Iraq have been supplied under the programme so far.

US defence contracts are BAE's single most important revenue stream.

Earlier this summer it lost out on a $3.3 billion US military deal to build all-terrain vehicles to protect troops against roadside bombs.