Associated Press A Palestinian boy runs away from Israeli soldiers stationed outside Yasser Arafat's compound in the West Bank town of Ramallah yesterday. A small group of youths throwing stones at Israeli troops set a car ablaze, drawing a few rounds of rubber bullets. The sign on the wall is part of a larger graffiti calling for the Intifadeh not to be forgotten.

JERUSALEM - A mysterious explosion killed two Palestinians and a third died in a clash with Israeli soldiers yesterday, while refugees in a West Bank camp that is a stronghold of militant gunmen built fortifications to fend off a feared Israeli invasion.

Tension ran high amid expectations of further violence. Because of the flare-up, U.S. officials put a truce mediation effort by envoy Anthony Zinni on indefinite hold.

In the Gaza Strip, the mangled bodies of two Palestinians were found after daybreak. The militant Popular Front for the Liberation of Palestine said the two were killed in a "heroic martyrs' operation." Israel radio said it was apparently a failed suicide bomb attack against a nearby Jewish settlement.

In the West Bank town of Ramallah, a Palestinian intelligence officer was killed in a clash with Israeli forces early yesterday. Israeli tanks are parked about 70 yards from Palestinian leader Yasser Arafat's headquarters there, holding him under virtual house arrest for the past two months.

Palestinian leaders say they can't enforce a cease-fire with Israel as long as Israeli troops maintain their siege of Ramallah and other West Bank towns and continue to kill suspected militants.

But the Palestinians got no support from Washington yesterday for their demand that the Israelis ease up on Arafat. White House spokesman Ari Fleischer said President Bush "understands the reason that Israel has taken the action that it takes, and it is up to Chairman Arafat to demonstrate the leadership to combat terrorism."

State Department spokesman Richard Boucher said there were no plans to send Zinni back to the region, despite a request from Arafat. In two visits over the past two months, Zinni failed to negotiate a truce.

Until recent weeks, the Bush administration had been highly critical of Israeli operations inside Palestinian-controlled territory. Israel's Jan. 3 interception in the Red Sea of an arms-laden ship, Karine A, which Israel claimed was run by the official Palestinian Authority and headed for Gaza, marked a shift in U.S. policy. The administration accepted the Israeli claim in the face of Palestinian denials.

In Gaza, about 1,500 Palestinians marched in support of Arafat yesterday. "We are protesting (Israeli Prime Minister Ariel) Sharon's crimes against our people and our beloved president," said law student Rami Abu Safiya, 24.

In Jenin, a stronghold for gunmen and bombers from militant Islamic groups at the northern edge of the West Bank, Palestinians were expecting an Israeli incursion.

Palestinians say about 300 militants armed with rifles and hand grenades have moved from the town into a nearby refugee camp, and refugees are building earthen ramparts up to 10 feet high across roads to keep the Israelis out.

About 13,000 refugees live in the camp. Up to now, Israeli forces have avoided entering refugee camps, where tanks cannot negotiate the narrow alleyways and soldiers would be at greater risk.

The Israeli military would not comment about Palestinian expectations of an incursion. Israeli forces have moved into Jenin briefly several times, destroying Palestinian police buildings in retaliation for bomb attacks. Last week, Israeli forces invaded nearby Tulkarem and held parts of it for a day as they searched for terrorist suspects.

In Hebron yesterday, Israeli soldiers disguised as Arabs arrested a suspected Palestinian militant. Palestinian witnesses said six soldiers, wearing traditional Arab headdresses, entered a bakery and shot Hazem Qawasmeh before arresting him.

Israeli military sources said the soldiers shot Qawasmeh in the leg after he tried to escape. The military said he was involved in dozens of attacks on settlers and soldiers, using bombs and firebombs he made.