"Insurgents are deploying huge, deeply buried munitions set up to protect their territory and mounting complex ambushes that demonstrate their ability to respond rapidly to U.S. tactics," writes the Post. "A new counterinsurgency strategy has resulted in decreased civilian deaths in Baghdad but has placed thousands of additional American troops at greater risk in small outposts in the capital and other parts of the country."

Insurgents are specifically targeting American soldiers, while attacks on Iraqi security forces are on the decline.

"The attacks are being directed at us and not against other people," said Major General James Simmons, who also said that attacks against US troops were up.

May, which was the third deadliest month for US soldiers in Iraq since the start of the war, was also highlighted by a dramatic fall in the ratio of wounded to killed. The ratio fell from 8 to 1, to 4.8 to 1, and indication that attacks on US soldiers were deadlier as well as more frequent.

That majority of US casualties are caused by roadside bombs. "Gains in defeating the bombs have not resulted in fewer deaths because the number of bombs -- and the lethality of some types -- have increased, military officials said," according to the Post.

Analysts expect the violence to continue. Already in June, nine US soldiers have been killed in the first two days, including seven in six separate incidents on Saturday.

"We are looking at a very nasty summer," said Toby Dodge, an Iraq expert at London's Queen Mary College University.