GAZA CITY, October 8 (IslamOnline & News Agencies) - The Palestine Liberation Organization (PLO) called Tuesday, October 9, on people "not to kill each other" following deadly clashes sparked by the murder of a police commander in the Gaza Strip.

The 11 groups making up the PLO also condemned in their statement "all attempts to sow discord" among Palestinians, after two days of sporadic street fighting between Hamas members and police that claimed the lives of four people, Agence France-Presse (AFP) reported.

"The blood of Palestinians is sacred, and Palestinian arms must be used solely against the Zionist enemy," they said, referring to the latest two-year Intifada against the 54-old Israeli occupation of Palestine.

Meanwhile, the National and Islamic Forces, an umbrella group of the 13 main Palestinian factions, including both Palestinian President Yasser Arafat's resistance Fatah movement and the Islamic resistance movement Hamas, met Tuesday night in Gaza City to calm the situation and reach an agreement.

A Hamas leader, Ismail Haniyeh, said the talks ended without any concrete agreement being reached, but stressed the session had been a productive one.

"Hamas and Fatah met tonight and agreed to continue dialogue about stopping the clashes," he told AFP by phone.

"We will continue in our efforts towards national unity and have agreed to have another meeting as soon as possible," Haniyeh said, adding he was "hopeful it would put an end to all the clashes".

Zakaria al-Agha, a Fatah leader in the Gaza Strip, earlier said Arafat's group insisted the police chief's killers be handed over.

According to the police, around 20 armed members of the Islamic resistance movement Hamas, disguised as national security officers, on Monday abducted and murdered the head of the Palestinian riot police, Brigadier General Rajeh Abu-Lehya in revenge for the murder of two demonstrators killed in anti-U.S. riots last October.

The Hamas cell was headed by the brother of one of the slain youths and the group said the killing was a family vendetta, a common occurrence in Gaza's clan-based society.

Clashes erupted shortly thereafter in and around Gaza City between police and Hamas members and supporters - clashes that claimed four lives and left dozens wounded. There were more clashes Tuesday, but no injuries were reported.

Hamas has denied it was involved in the killing of the police commander and called the affair a settling of scores between families of the protestors killed last year and police.

The PLO groups denounced Abu-Lehya's killing as an "odious crime ... committed in cold blood" and demanded that the killers be brought to justice.

The main groups in the PLO are President Arafat's Fatah faction, and the Popular Front for the Liberation of Palestine and the Democratic Front for the Liberation of Palestine (PFLP).

The increasingly popular Islamic resistance groups Hamas and Islamic Jihad are not part of the PLO.

At the time the Palestinians are busy with an internal conflict, the Israeli occupation army killed two Palestinian boys and wounded dozens more youths Wednesday, showing no sign of easing its aggression in Gaza despite repeated U.S. calls for restraint.

While taking some steps to appease mounting criticism from U.S. President George W. Bush, who is seeking calm on the Israeli-Palestinian front as he prepares for a possible war on sanction-hit Iraq, Israel's far-right Prime Minister Ariel Sharon remained defiant.

In the southern Gaza Strip town of Rafah, tanks, escorting bulldozers demolishing Palestinian houses along the Israeli-controlled border with Egypt, opened fire and killed two Palestinian teenagers, medical sources said.

A crowd of angry stone-throwers which gathered following the murder of the first boy, was targeted by another burst of heavy machine-gun fire from the tanks that killed the second.

About 20 youths were wounded in the incident, 10 of them seriously, only two days after a deadly Israeli army raid into the nearby town of Khan Yunis killed 16 Palestinian civilians, drawing fierce international condemnation.

The deadly Monday raid drew condemnation from both the United Nations and the European Union.

The assault, which included tanks, bulldozers and helicopters, also met with severe reprobation from the White House, where Sharon is due to hold talks next week, and sparked Palestinian fears of a reoccupation of Gaza.

Sharon shrugged off Washington's "deep concern" and said his raids would continue, qualifying Monday's pre-dawn operation as a "success".

In further Gaza violence, Israeli fire ripped through a school in Khan Yunis on Wednesday, injuring eight Palestinians, including four schoolboys, Palestinian security sources said.

On Tuesday, a 12-year-old Palestinian girl was shot dead in Rafah.

Meanwhile, in a bid to appease international ire over its assaults on Palestinian civilians in the occupied territories, the Israeli army moved to demolish what they call unauthorized outposts built by Jewish settlers in the West Bank.

At least two unoccupied outposts were dismantled near Nablus on the orders of Defense Minister Binyamin Ben Eliezer, who reportedly plans to proceed with the demolition of up to 30 such sites, including some which are inhabited.

Built without permission on Palestinian land occupied by Israel in the 1967 Middle East war, they are usually tiny makeshift settlements made up of caravans, after which permanent buildings and security installations are slowly added.