Baghdad, Iraq ? Bomb blasts killed six Marines as the U.S. military announced Friday it had completed a major sweep in western Iraq aimed at suppressing al-Qaida militants before next week’s vote on Iraq’s constitution.

The military said 50 insurgents were killed in the six-day offensive, launched Oct. 1 in towns near the Syrian border. The operation was the first in a series of major offensives in the past week in the heartland of the Sunni-led insurgency.

U.S. forces have swept through the area before – most recently in May – but militants have always returned, bringing in foreigners from Syria and planning attacks to be carried out elsewhere. The military said they will now leave a long-term presence there.

The military has said it will wrap up the operations in time for Sunni Arabs in the region to vote in the Oct. 15 referendum, a key concern of Sunni leaders who have threatened a boycott.

Eight days before Iraqis were to approve or reject the draft constitution, most were still waiting for copies of it to read. Distribution began in a few Baghdad neighborhoods, but did not appear to have begun elsewhere.

Campaigning has begun in earnest, however, with radio and television running call-in and talk shows on the document, which has strongly divided Iraq’s Shiite majority and Sunni minority. Shiite and Kurdish leaders support the constitution – whose passage the United States is eager to see – while Sunnis denounce it, saying it will split the country.

In the hours before the offensive’s end, a roadside bomb killed two Marines outside Qaim, near Sadah, the military said.

Closer to Baghdad – away from the offensives – a roadside blast Thursday killed four Marines in Karmah, outside the city of Fallujah, the military said.

The deaths brought to 1,950 the number of U.S. service members who have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

The 1,000 Marines, soldiers and sailors involved in Iron Fist killed some 50 insurgents, the military said. On Thursday, warplanes dropped four precision-guided bombs on an abandoned hotel seized by militants in the town of Karabilah, near Sadah, killing 20 militants.