A Palestinian civilian was killed on Tuesday when President Mahmoud Abbas's security forces clashed with gunmen for the first time since launching a law-and-order push in the northern West Bank.

Hundreds of Abbas's forces deployed to the city of Jenin on Saturday in a U.S.-backed security push Washington hopes will show the Palestinians can rein in militants - Israel's main condition for Palestinian statehood.

Residents in the town of Qabatya near Jenin said civilian Ahmed Fawwaz Kmeil, 20, was shot as he tried to escape a standoff between Abbas's forces and local gunmen who were sitting in a cafe.

Palestinian forces said in a statement the man was killed when an "outlawed group" opened fire on the security men, adding they would investigate the incident and keep up their crime-fighting push.

The Jenin deployment by Abbas's forces, some of whom receive U.S.-funded training in Jordan, was the second big Palestinian security campaign in a major West Bank city following a similar mission in Nablus late last year.

Jeeps and buses which commanders said carried up to 600 security men arrived in the city on Saturday in coordination with Israel. Another 150 men already in Jenin, long a militant bastion, have joined them.

The forces also entered the restive Jenin refugee camp - the first Palestinian security men to do so. They had planned to remain in Qabatya for a few days in a show of force but withdrew to the entrance of the town fearing tension after the killing.

Powerful clans including the Kmeils have long ruled Qabatya and the incident could spark tension between the family and the new force. Its commanders said they are determined to impose law and order and confiscate illegal weapons, even by force.

The new force plans to enter some 50 villages around Jenin for similar missions.