It was yet another psychological blow to US forces in Iraq, as four more soldiers fell prey to extremist fury in southern Iraq on Sunday -- the number of American casualties touching the 4,000 mark.

The development comes a week after US President George Bush [Images], while addressing the media on the fifth anniversary of the Iraq war, said that the increase of 30,000 troops that he ordered to Iraq last year has turned 'the situation in Iraq around'.

The US has about 1,58,000 troops in Iraq. The number is expected to drop to 140,000 by mid-year.

CNN reported that critics had been charging that the Iraq war had become a breeding ground for terror, even as opinion polls suggested that US public support for the war had been waning.

Image: Thousands of crosses adorn a hillside in Lafayette, California, in memory of US troops killed in Iraq.
Photograph: Kimberly White/Getty Images