Eight American soldiers were killed in roadside bombings and a helicopter crash in Diyala, north of Baghdad, the US military said today, making May the deadliest month of the year so far for US forces in Iraq.

The soldiers — from Task Force Lightning — were all killed on Monday as the America marked Memorial Day, its day of remembrance for the military.

In statements issued today, the military said six of the soldiers died in a single patrol and two others were killed when their helicopter came down in Diyala, the unstable province north of Baghdad that has experienced an increase in violence since the start of the joint US-Iraqi security operation in February.

The casualties bring the US military death toll to 110 for May, of whom a fifth have died in Diyala, a province with a mixed Sunni and Shia population and a landscape of thick orange groves and date palms that has proved fertile territory for the guerrilla tactics of insurgents attacking US patrols.

US commanders have acknowledged that the security operation in Baghdad and the influx of extra troops, as part of President Bush's surge plan, into the western province of Anbar have helped push insurgents into the less heavily patrolled Diyala but say they are redressing the imbalance.

Earlier this month, Major General Benjamin Mixon, the commander of northern Iraq, said: “I do not have enough soldiers in Diyala province to keep that security situation moving."

In America, the anti-war movement suffered a blow today when Cindy Sheehan, a mother whose son died in Iraq and whose camping outside Mr Bush's ranch in Texas helped galvanise protests against the war last summer, said she was giving up her campaign.

Mrs Sheehan, whose marriage failed as she doggedly attended rallies and vigils up and down the country, said she had decided to give up because she had failed to receive enough support from the Democratic Party and American liberals.

“I’m going home for awhile to try and be normal,” she wrote in what she described as a “resignation letter" on the liberal website, the Daily Kos. “Good-bye America... You are not the country that I love and I finally realised no matter how much I sacrifice, I can’t make you be that country unless you want it. It’s up to you now.”

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