Baghdad, Iraq ? U.S. and Iraqi troops launched a fresh attack Monday against an insurgent stronghold near the Syrian border despite calls by Sunni Arab leaders to halt such operations to encourage a big turnout in next month’s election. The U.S. command said about 50 insurgents were killed.

Two U.S. Marines were killed and at least seven were wounded in the fighting in the border town of Obeidi, according to a New York Times reporter is embedded with the Marines. A Marine spokesman told The Associated Press that he cannot report casualties until 24 hours after they occur.

In Baghdad, a car bomb exploded near the main gate to the heavily guarded Green Zone, killing two South Africans and wounding three other people. The victims worked for State Department security contractor DynCorp International, the U.S. Embassy said.

The U.S.-Iraqi attack against Obeidi was the latest stage of an offensive to clear al-Qaida-led insurgents from a string of towns and cities in the Euphrates River valley near the border with Syria and seal off a major infiltration route for foreign fighters sneaking into Iraq.

“Approximately 50 insurgents are estimated to have been killed in sporadic but heavy fighting,” a U.S. statement said. Most of the insurgents died in at least five U.S. airstrikes.

U.S. forces remove a damaged vehicle after a car bomb detonated Monday near a security convoy killing two South Africans and wounding three others outside a gate leading into the fortified Green Zone, the headquarters of the Iraqi government and U.S. forces, in central Baghdad, Iraq.

Earlier this month, U.S. and Iraqi forces overran two other towns in the area – Husaybah and Karabilah. Unlike in previous sweeps in the area, the Americans and their Iraqi allies plan to establish a long-term presence to prevent insurgents from returning.

U.S. officials have said the Euphrates Valley campaign is also aimed at encouraging Sunni Arabs there to vote in the Dec. 15 parliamentary elections without fear of insurgent reprisals. The Bush administration hopes that a successful election with strong Sunni Arab participation will encourage many in that community to abandon the insurgency.

That in turn would make it possible for U.S. and other international troops to begin heading home next year. Iraqi President Jalal Talabani said Monday in Vienna, Austria, that talks on a withdrawal schedule could begin late next year.

The Baghdad blast occurred about 100 yards north of the main gate to the Green Zone, headquarters of the Iraqi government and the U.S. mission. The blast, which targeted the security convoy as it left the Green Zone, was followed by small arms fire which echoed through the heart of the capital.

Two Apache attack helicopters flew over the scene as thick black smoke cleared.