The American deaths brought to 1,950 the number of US troops who have died since the beginning of the war in 2003, according to an Associated Press count.
In southern Iraq, British troops detained 12 militia men loyal to a radical Shi'ite cleric in the city of Basra, accusing them of carrying out recent attacks on British and US troops, amid charges Iran is helping fighters to carry out deadlier bombings.
Eight days before Iraqis were to go to the polls to approve or reject the new constitution, officials across the country were still waiting to get copies of the document to pass out to voters. Distribution began in a few Baghdad neighbourhoods, but did not appear to have begun elsewhere.
Some shopkeepers in Baghdad refused to hand out the document and some people refused to take it, fearing reprisals by militants determined to wreck the crucial October 15 referendum.
Al-Qaida in Iraq and other Sunni-led insurgent groups have launched a wave of violence that has killed more than 290 people the past two weeks, many of them Shi'ites in brutal bombings and shootings at a mosque, a bus and a school. Al-Qaida in Iraq leader Abu Musab al-Zarqawi has declared war on Iraq's Shi'ite Muslim majority.
The Pentagon said yesterday that the military in Iraq had intercepted a letter from the second in command of al-Qaida, Ayman al-Zawahri, to al-Zarqawi, urging him to avoid bombing mosques and slaughtering hostages to avoid alienating the masses.
Pentagon spokesperson Bryan Whitman said the letter also demonstrates "detailed planning and intent on the part of the insurgents in Iraq to one day control that country and to really try to extend their extremism to neighbouring countries."
The US military is waging two large offensives in western Iraq operations Iron Fist and River Gate to oust al-Qaida-in-Iraq militants from six towns along the Euphrates River valley.
Two marines were killed on Thursday by a roadside bomb that hit their patrol outside the town of Qaim, the region near the Syrian border where Iron Fist is being waged, the military said. Their deaths bring to six the number of US troops killed in Iron Fist and River Gate.
Apart from the offensives, four marines were killed Thursday by a roadside bomb in Karmah, near the town of Fallujah, 64 kilometres west of Baghdad.
The 29 deaths raised the insurgent death toll in Iron Fist to 71. At least six insurgents have been reported killed in River Gate offensive, taking place some 129km south-east down the Euphrates.
The British raid in Basra targeted a house and netted 12 members of the al-Mahdi militia, the armed force loyal to radical Shi'ite cleric Muqtada al-Sadr, said a British military spokesperson.
In new violence in Baghdad, at least seven Iraqi civilians were killed in shootings around the city, and at least two bodies were found dumped.