Abu Yousef Abu Quka's death in a car bomb Friday posed the first direct threat to the Hamas government, just two days after the Islamic group assumed power. The militant's followers blamed the attack on security forces loyal to Palestinian President Mahmoud Abbas' Fatah movement.

The killing set off gunbattles that left three people dead, wounded 36 and raised the possibility of wider clashes.

Prime Minister Ismail Haniyeh said it was "a dangerous situation and shouldn't happen again." He said security forces would try to "pull our civilian gunmen off the streets," though he did not specify which armed men or elaborate on a plan.

Abu Quka was a senior commander of the Popular Resistance Committees, an umbrella group of about 200 gunmen linked to explosions of Israeli tanks and a deadly attack on a US diplomatic convoy in 2003. About half the group's gunmen are allied with Hamas and the other half with Fatah.

Hamas has pledged to restore order in the West Bank and the Gaza Strip, which has been plagued by increasing lawlessness, with gunmen roaming the streets with impunity.

Hamas, however, has little control over most Palestinian security forces, which are affiliated with Fatah and have been involved in some of the violence.

Abbas, a moderate who favours peace talks with Israel, is a vocal critic of violence but has struggled to gain control over the security forces since his election last year.

On Friday, Haniyeh ordered an investigation and urged calm.

"I want to stress the need not to slide toward civil war," he said in a televised interview. "Let us not direct our arrows at each other."

Hamas' interior minister, Said Siyam, who is in charge of several security agencies, promised to bring Abu Quka's killers to justice.

The Popular Resistance Committees initially blamed Israel, which denied involvement, and then pointed to the Preventive Security Service.

Gunfire broke out at the funeral. Hospital officials said three people were killed, including two bystanders and a PRC member who had joined the procession. Thirty-six others were wounded, six critically, they said.