The five Iraqi soldiers were taken to a Baghdad hospital, an Iraqi Interior Ministry source said, adding that the attack happened at about 8.30am (0430 GMT) on Thursday behind a police station in the northern Sulaikh district.
US military sources, in a statement on Thursday, gave no details of the attack on the marines, which was carried out on Wednesday. It is the second time in a week that fighters have inflicted such a high death toll on marines in the same area in a single blast.
Twelve Iraqis were also killed, among them a judge and four children, and six other Iraqis wounded, in separate car bomb attacks in Baghdad and Kirkuk, reported Aljazeera.
Aljazeera's correspondent Udei al-Khatib said most of the deaths occurred when a booby-trapped car blew up on Baghdad's airport road which is now called the "death road".
In Falluja, a bomb blew up in Nizal neighbourhood in the centre of the town wounding two Iraqis. They were taken to hospital, reported al-Khatib.
US officers have said some rebels have been using "shaped charges", which concentrate blasts on to a small area, allowing them to penetrate the heavy armour of tanks.
Improvised explosive devices, as the troops call them, are the biggest threat to Americans in Iraq. Though many are spotted and defused, dozens go off every day.
The road to Baghdad airport is
now nicknamed Death Road
The US military has strengthened the armour on all its vehicles, at considerable cost in both equipment and in added fuel bills for the heavier loads.
Al-Zarqawi aide held
Meanwhile, US forces announced they had detained a senior associate of Jordanian fighter Abu Musab al-Zarqawi.
Brigadier-General Donald Alston told a news conference on Thursday that the arrest was a major blow to the anti-US campaign in the northern city of Mosul.
Mohammed Khalif Shaiker, also known as Abu Talha or the Amir of Mosul, was captured on Tuesday in a quiet neighbourhood of Iraq's third largest city.
US and Iraqi security forces have announced the arrest of several senior associates of al-Zarqawi in recent weeks.
In a separate incident, armed pirates raided a supertanker anchored close to Iraq's Basra oil export terminal in the early hours of Wednesday, in the latest serious security breach at the facility, local ship agents said.
Gulf Agency Company (GAC) said the raid comes only two weeks after pirates attacked the crew of a supertanker waiting to load crude oil at the southern deep-water terminal where most of Iraq's crude oil is exported.
Senior associates of al-Zarqawi
have been arrested recently
Exports from Basra provide nearly all of Iraq's income.
In Geneva, a former top UN humanitarian official in Iraq on Thursday called for an end to a UN programme exacting compensation from Iraq for its 1990 invasion of Kuwait and the Gulf war.
Hans von Sponeck, who quit as UN humanitarian coordinator
in 2000 after sharply criticising the effects of the then
economic sanctions on civilians, said Iraq's government should
negotiate its reparations debt directly with claimants.
The UN Compensation Commission, set up by the Security
Council to compensate losses using a share of Iraqi oil sales,
has approved $52.1 billion in payment to individuals, companies and governments so far.
Its Governing Council is due to approve a final batch of
claims at a meeting later this month.