The United States cannot keep up with military demand for ammunition which has more than doubled since the war on terrorism and the invasion of Iraq were launched, according to a Congress watchdog report released Wednesday.

The report said that the amount of small ammunition needed had increased from about 730 million rounds a year to nearly 1.8 billion.

For medium calibre ammunition, the rise had gone from 11.7 million rounds to almost 22 million, said the General Accounting Office.

Defence Department purchases of ammunition had reduced after the end of the Cold War and a number of government owned production factories were closed, said the report by the Congress watchdog.

The department has spent more than 90 million dollars on improvements at the remaining three main facilities for small and medium calibre bullets in a bid to boost production.

But supplies of small sized ammunition is lagging behind demand and the United States is now relying on foreign producers, including from Israel, to help meet its needs.

"Unforeseen events such as the terrorist attacks of September 11, 2001 and subsequent military deployments, make predicting future requirements difficult," said the GAO.

"However it is imperative that the warfighter be provided with sufficient ammunition to carry out missions to counter ongoing and emerging threats without amassing wasteful unused stockpiles."