Gunmen killed a colonel in the Palestinian security forces early on Wednesday when they raked his car with gunfire in the northern West Bank city of Jenin, local officials said.

Hisham al-Rukh was attacked while driving home in the Jenin refugee camp, which has been the focal point of a broad sweep by security forces since May following an upsurge of violence led by criminal gangs and corrupt security officers.

The incident follows an attack last month in the centre of Ramallah, the West Bank's de facto capital, when gunmen opened fire on Palestinian Prime Minister Salam Fayyad's offices. No one was injured.

"An investigation is being undertaken to find out who is behind this incident," Jenin Governor Talal Dweikat told Palestinian radio after the shooting.

Dweikat's predecessor died of a heart attack after chasing unidentified gunmen who attacked his home in early May. Palestinian officials blamed the attack on criminal gangs, weapons smugglers and former militant leaders whom they suspect of having ties with rogue members of the security forces.

In response to the May attack the Palestinian Authority ordered its elite forces to expand the crackdown beyond Jenin to other West Bank cities and camps.

Wednesday's shooting undermines the campaign and a drive to impose the authority of Palestinian security forces throughout areas under the Authority's control in the occupied West Bank.

Israel largely crushed a Palestinian uprising and campaign of attacks against it in the early years of the past decade through overwhelming military incursions into the West Bank, and especially Jenin.

The Palestinian Authority has struggled to rein in former militant leaders, and the security personnel widely believed to be backing them, following the Israeli withdrawal.

Meanwhile, an ultraconservative Islamic group said Hamas security forces have detained 20 of its members in a crackdown on rocket fire from Gaza on southern Israel.

 The little-known group, the Mujahadeen Shura Council of Jerusalem, posted word of the sweep on its website on Wednesday. It said its members were rounded up this week "to prevent rocket fire from Gaza."

The crackdown is the first in more than a year on ultraconservative Salafi groups operating in Gaza. Hamas currently is believed to be interested in avoiding a conflict with Israel over rocket fire.

The Muhahadeen Shura Council of Jerusalem claimed responsibility for a deadly infiltration into Israel along its border with Egypt's Sinai Peninsula in June, which killed an Israeli Arab.