US President George W Bush is expected to announce reinforcements for Iraq but Clark said the time for a military solution was past and a region-wide initiative was needed to try to end the bloody sectarian violence.

Such a recommendation was put forward in the US Iraq Study Group report last year and has been backed by Bush's key ally in Iraq and the so-called "war on terror", British Prime Minister Tony Blair.

"We've never had enough troops in Iraq," Clark, the former Supreme Allied Commander of Nato forces from 1997-2000, wrote in Britain's Independent on Sunday newspaper.

"In Kosovo, we had 40,000 troops for a population of two million. For Iraq, that ratio would call for at least 500,000 troops, so adding 20,000 now is too little, too late.

"What the surge would do is put more American troops in harm's way, further undercut US forces' morale, and risk further alienation of elements of the Iraqi populace."

News reports in the United States last week said Bush would announce an increase in troop numbers in the coming days, estimating the figure between 9,000 and 40,000. Several outlets put the numbers at 20,000.

There are currently 132,000 US troops in Iraq as well as 17,000 members of the US-led coalition from 25 other countries, the Pentagon said Thursday.