Israeli soldiers faced the toughest resistance yet in their West Bank offensive, trading round-the-clock fire with Palestinian gunmen Saturday in Nablus and Jenin. Without giving a time frame, Israel's leader told President Bush he would expedite the nine-day offensive.

Israeli soldiers were again unable to take full control of the two cities for a third straight day of fighting.

With the gunmen firing from apartments and homes along narrow streets and alleyways, Israeli troops faced the toughest resistance yet in the offensive. The Israeli troops have taken only parts of the two cities and have not entered the nearby refugee camps, which are strongholds for the militants. One Palestinian fighter said bombs and weapons were being passed out to residents to defend the camps.

Bush repeated his call for Israel to "withdraw without delay" from towns it has occupied since launching its offensive to crush Palestinian militias after a string of suicide attacks. Speaking alongside British Prime Minister Tony Blair, Bush also demanded the Palestinians call "an immediate and effective cease-fire."

Israeli leader Ariel Sharon spoke with Bush by phone Saturday and told the American leader that Israel will expedite its offensive. In a brief statement, Sharon's office said he told Bush that Israel "is conscious of the American desire to see the operation end quickly."

Sharon's statement, however, did not say when they would withdraw troops in the operation launched March 29. He said Israel is operating in difficult conditions in areas where "there are a great deal of weapons, explosives and armed terrorists." Sharon stressed that Israel is making every effort to avoid civilian casualties and that this caution is making the operation last longer.

Bush is dispatching Secretary of State Colin Powell to the region this coming week, but the mission is already facing one potential problem: The Palestinians said Saturday they won't talk to Powell unless he meets Arafat.

Meanwhile, Israeli troops and Palestinian security forces had a brief but intense exchange of fire Saturday night at the besieged compound of Palestinian leader Yasser Arafat.

Nabil Aburdeneh, an Arafat spokesman in the compound, said Israeli troops made moves to enter Arafat's office, prompting the Palestinian guards in an adjacent building to open fire. The Israelis shot back at the security guards, wounding four, one of them seriously, he said. No one in Arafat's office was hurt, he added.

The Israeli army said it came under fire from the building next to Arafat's office and returned fire with weapons that included an anti-tank missile.

A Palestinian ambulance picked up the Palestinian security guard who was seriously hurt, but Israeli troops forced rescue workers to hand him over. The unidentified guard, who was wanted by Israel, was taken to an Israeli hospital for treatment, the army said.

Overall, 17 Palestinians and one Israeli soldier were killed Saturday, with most of the deaths in Nablus and Jenin, which are 15 miles apart in the northern part of the West Bank.

The fighting in those two cities was in sharp contrast to that in other parts of the West Bank since Israel launched its invasion last month, after a series of suicide bombing attacks that killed scores of Israelis. In most areas, Israeli tanks and armored personnel carriers faced very limited resistance and quickly took charge of the streets, with Palestinian residents remaining inside and under curfew. Still, the nine-day-old incursion has left at least 74 Palestinians and 10 Israeli soldiers dead.

In Jenin, Israeli troops on the edge of the city's refugee camp have been battling gunmen round the clock. The Israeli forces have entered some city neighborhoods, but are facing resistance in the eastern part of the city, residents said.

Jamal Abu al-Haija, a leader of the militant Hamas movement in Jenin, said militant factions had banded and were distributing weapons -- including explosive belts like those used by suicide bombers -- to residents of the nearby refugee camp. "All the factions have distributed explosive belts and hand grenades to the people of the camp to defend themselves," he said by telephone.

A Palestinian woman in Jenin camp, Ilham Dosuki, blew herself up early Saturday when soldiers approached the door to her home, according to al-Haija, who said the bombing caused casualties among the soldiers.

The Israeli military reported a somewhat similar event, saying troops fired on a Palestinian wearing explosives. The gunfire caused a blast that killed the attacker, whom they identified as a man. No soldiers were hurt, the army said.

In Nablus, the Israeli forces have been sending in helicopters that fire machine guns or rockets in an attempt to dislodge the gunmen. The Israelis have taken over many parts of Nablus, but have only edged into Nablus' Old City, where they have encountered heavy shooting. The Israelis have surrounded the Balata refugee camp on the outskirts of Nablus and waged fierce firefights, but have not gone into the camp, Palestinian witnesses said.

Nablus and Jenin both have large numbers of militants, and many of the Palestinian suicide bombers have come from these two cities, Israel says. The narrow streets make it impossible to enter parts of the two cities and too dangerous for ground troops to enter on foot.

Facing growing international calls to end its incursion, Israel says it won't pull out until it feels it has substantially dismantled the Palestinians' ability to carry out suicide bombings and other attacks.

"I believe it will last until we finish it," said Maj. Gen. Dan Halutz, head of the Israeli air force, adding that top military officials have spoken of a four-week operation. "The length of the operation is not a military decision, it's a military request, but a government decision."

In Bethlehem, a standoff dragged on for a fifth day between Israeli forces and scores of Palestinian gunmen holed up in the Church of the Nativity, which marks the site where tradition says Jesus was born.

Five people left the church Saturday and were taken away by Israeli soldiers in an armored personnel carrier. They included two Greek Orthodox priests, a nun and an elderly woman and her daughter, according to Lt. Col. Olivier Rafowicz, an Israeli army spokesman.

An estimated 200 Palestinian gunmen entered the church Tuesday to escape Israeli troops closing in on them.

The Israeli-Palestinian fighting has been largely confined to the West Bank in recent days, but violence also erupted Saturday in the Gaza Strip.

Two Palestinian militants and one Israeli soldier were killed when the Palestinians attacked a heavily fortified Israeli settlement in the Gaza Strip early Saturday with guns and grenades, according to Israeli army officials. The militant group Islamic Jihad claimed responsibility for the attack, which also wounded four Israeli soldiers.

Also, four Palestinian civilians, including girls aged 5 and 12, were killed by Israeli army fire in Rafah, a town at the southern end of the Gaza Strip, according to Palestinian witnesses and doctors. The Israeli army said there was an exchange of fire in the area, but had no information on casualties.