The US military said two of the powerful bombs targeted suspected safe houses near the town of al-Qaim, a stronghold of anti-US fighters on the Euphrates river about 20km east of Iraq's border with Syria.
Four more were aimed at fighters as they fired mortars and
assault rifles at US ground forces near al-Qaim, and a further
three were used to hit suspected weapons caches in the area.
The air power was in support of Operation Spear, the third
major offensive US forces have launched in western Iraq in the past six weeks with the aim of crushing the fighters in the Euphrates valley which stretches northwest to Syria.
"Operation Spear ... began in the early morning hours with
the objectives of rooting out insurgents and foreign fighters
and disrupting insurgent support systems in and around
Karabila," Captain Jeffrey Pool of the US Marines said in a
statement from Ramadi, capital of the surrounding Anbar region.
Iraqi troops and US tank and amphibious assault units were
involved, he added. About 1000 troops were taking part in all.
US-led forces are trying to root
out fighters from al-Qaim
Residents in Karabila, a suburb of al-Qaim where the suspected weapons caches were targeted, said fierce gunbattles broke out overnight and continued.
In an earlier operation, on 11 June, 40 fighters had been killed in the same area.
A modified US Black Hawk helicopter, known as a Pave Low, made an unscheduled landing near Qusayba, 20km west of al-Qaim, the military said.
Captain Pool emphasised that it was not shot down.
The representative in al-Qaim of the Association of Muslim Scholars, Iraq's leading Sunni organisation, Mudhafar al-Ani, said he was calling for businesses to remain closed and residents to stay in their homes after weekly Friday prayers in protest against US action, which, he said, was endangering civilians.
"The US forces are escalating the situation and we will declare a general strike after Friday prayers," al-Ani said.
"The US forces are escalating the situation and we will declare a general strike after Friday prayers"
AMS representative in al-Qaim
The chief doctor at al-Qaim hospital, Hamdi al-Alusi, said six dead bodies had been brought to the mortuary on Friday, including one of a woman.
The identities of the five men were yet to be released. Al-Alusi said he believed they were killed during the bombings.
The operation came one day after Air Force Brigadier-General Don Alston called the Syrian border the worst problem in terms of stemming the influx of foreign fighters to Iraq.
Washington has been applying intense pressure on Syria to tighten control of its 611km border with Iraq.
The marine death toll in Iraq has risen sharply over the past few months and especially in the Anbar province over the past week.
US forces said they had lost 11 men and two sailors over the past week in separate incidents around Anbar.