NABLUS: Israeli troops killed six Palestinians in two separate operations on Saturday, including a West Bank raid the Palestinian Authority condemned as a "dangerous escalation."

It was the highest toll of Palestinians killed by Israeli forces in a single day since a 22-day Gaza war launched one year ago tomorrow, and came as tensions grew between Israel and the Western-backed Palestinian Authority.

Israeli jeeps roared into the historic Old City of the West Bank town and troops barged into three houses where they shot three members of president Mahmud Abbas's Fatah movement, witnesses said.

The army said the three had killed an Israeli West Bank settler on Thursday when they sprayed his vehicle with bullets and that one of them, Anan Subuh, 36, was in a hiding place and armed with a handgun.

Another militant, Raid al-Surakji, 40, used his wife as a shield when troops stormed his house, the military said. Soldiers opened fire, killing him and wounding the woman with a shot to the leg.

Family members said the troops entered without warning and killed all three men in cold blood, insisting none resisted arrest or opened fire.

This prompted the Israeli human rights organisation, B'Tselem, to call for an investigation into the killings, saying they could have been in fact "executions."

"Based on testimony from the site (of the raids), it appears that at least two of the three men were not armed and that they were shot and killed as they tried to surrender," B'Tselem spokeswoman Sarit Michaeli told AFP.

"There are good reasons to believe that these were executions."

Israeli military spokesman Peter Lerner confirmed none of the men fired any shots but said they refused to surrender and were considered "armed and dangerous."

"These were not people handing out roses or flowers, these are people who are shooting at Israelis driving on the road," he told reporters. "We don't wait to be shot at if we have a threat."

Subuh was a member of Fatah's armed wing, the Al-Aqsa Martyrs' Brigades, while the two others were party activists, said a Palestinian security official who asked not to be named.

Lerner said Palestinian security forces were informed of the raid just before it happened.

Palestinian prime minister Salam Fayyad denounced the operation as a deliberate attempt to undermine recent security gains.

"This operation represents a dangerous escalation, and can only be seen in the context of targeting the security and stability that the Palestinian Authority has been able to bring about," he said.

Abbas's spokesman Nabil Abu Rudeina accused Israel of trying to "drag our people into a spiral of bloody violence."

At funeral processions for the three men, hundreds of people took to the streets, chanting "With our souls, with our blood we sacrifice for you, martyrs."

The Islamist Hamas movement ruling Gaza said Abbas' "illegitimate" government was partly to blame for the killings because of its cooperation with Israel.

The spike in violence in the West Bank comes after more than two years of relative calm during which Palestinian security forces loyal to Abbas restored law and order in several former militant strongholds.

Israel has in turn lifted some of its hundreds of checkpoints and roadblocks and scaled back military operations in the West Bank.

Nablus saw heavy fighting during the 2000 intifada, or uprising, but has more recently calmed down and been held up as a model of the Palestinian Authority's commitment to the peace process with Israel.

Meanwhile, another three Palestinians were killed in an air strike on Gaza, local medics and the Israeli military said.

A military spokeswoman said the three were militants who ignored warning shots, but medics and Hamas border guards stationed nearby said they were civilians scavenging for scrap metal.

Gaza, which Hamas seized from Fatah forces in June 2007, has been relatively calm since a January 18 ceasefire ended Israel's massive 22-day offensive aimed at halting Palestinian rocket attacks.

Some 1,400 Palestinian and 13 Israelis were killed and entire neighbourhoods were flattened in what was the deadliest Israeli offensive ever launched on the territory.