A modest stone building holy to Jews in the midst of this Arab city is becoming an increasingly volatile friction point, drawing growing numbers of pilgrims on nighttime prayer visits, unnerving Palestinian residents and putting Israel's military into conflict with some of the worshippers it is meant to protect.

The monthly trips by religious Jews to this largely hostile city, coordinated with Palestinian security forces, emphasize the complexity of the Holy Land's religious landscape and the sometimes deadly intersection of the sacred and the political.

Just after midnight Monday, convoys of buses carrying 1,600 Jewish worshippers began driving into Nablus in waves for prayers at Joseph's Tomb. Escorted by olive-drab army jeeps and dozens of ground troops, it was the biggest group to reach the site since the military began regularly allowing visits four years ago.

The lead bus was crammed to perhaps twice its capacity with ultra-Orthodox Jews in long black coats, settler teens in jeans and T-shirts, and girls in long skirts. There was an air of anticipation and, as time wore on, a sour smell of perspiration.

When the buses finally moved into Nablus, Israeli soldiers in battle gear were visible securing the route, standing by closed shops and clumped beside a Bank of Palestine ATM.

Organizers, members of the hard core of Israel's settlement movement, see the visits to the traditional gravesite of the biblical Joseph as a mix of religious duty, assertion of ownership and show of force. For many observant Jews, Nablus is part of the biblical land promised to the Jews by God.

"These are our roots," said Gilad Levanon, a 22-year-old Jewish seminary student, who was among the worshippers this week. "We have a strong belief that this is our role in this world — to continue the path of our fathers, despite momentary interference."

Palestinians view them as a provocation and an attempt by Israeli extremists to create a political foothold inside their city, which is one of the main autonomous zones established by the interim peace accords of the 1990s. The Palestinians hope to make the entire West Bank, captured by Israel in the 1967 Mideast war, part of a future independent state.

"If a believer wants to worship God, he can do that from any place," said Zuheir Dubei, 58, a mosque preacher in Nablus, "not only from a place like Joseph's Tomb where blood can be shed."

There are always more would-be worshippers than places on the buses, and people often spend months on a waiting list, said David Haivry, a settler spokesman and convoy organizer.

Some worshippers, including about 200 young men on Monday, have made a point of sneaking into Nablus without permission, forcing the army to play a game of nocturnal cat-and-mouse with them in the fields around the city. Last month, a 25-year-old Israeli man traveled to the tomb without permission and was killed by a Palestinian policeman.

In coordination with the military, Palestinian security forces are pulled off the streets when the worshippers go in to avoid clashes with the Israelis, and the streets were empty when the first buses arrived. The only explicit sign that the city of 125,000 was inhabited came in the form of a lone rock that slammed into the side of the lead bus as it passed a row of homes.

The first to leap out when the bus pulled up outside the domed tomb was a young man with red sidelocks who wore the long black gabardine of the Bratslav Hasidic sect. He sprinted for the tomb, joined by streams of worshippers who poured out of the buses, ran through the gate and pressed ecstatically into the small room that houses the grave marker to chant psalms. Hebrew graffiti on one wall read, "Joseph lives."

Some visitors openly lamented the fact that they could not freely access the tomb whenever they pleased. "We're still coming at night, like dogs," one bearded man said.

The tomb area assumed an air of anarchic festivity as the center of a silent Palestinian neighborhood, between a girls' school and a shuttered candy kiosk, became the temporary domain of the Israeli religious right: a crush of black-clad men singing Hebrew songs, middle-aged women, cigarette-smoking youths and teenage girls in Ugg boots.

One man dressed entirely in white banged a drum, stopping just long enough to blow a shofar, a traditional ram's horn. There were the velvet skullcaps and black hats of the ultra-Orthodox, the enormous knitted skullcaps of settler hard-liners, and the berets and helmets of heavily armed soldiers.

A nighttime observer might not recognize the tomb area in daylight.

On a morning earlier this month, the tomb was empty, guarded by two sleepy Palestinian policemen in a pickup truck. The sound of children was audible from the school, and Raji Barah, 43, was selling candy and drinks from his kiosk.

Barah said he had been questioned by Israeli soldiers after the Jewish worshipper's death two weeks earlier.

"They said, 'Did you see the one who fired?' I said, 'I didn't see anything,'" Barah said.

Nablus was a militant hotbed in the years of the Palestinian uprising last decade. The city's Palestinians and the residents of nearby settlements, considered hard-line even by many other settlers, view each other with deep animosity.

To secure the Jewish worshippers, the military takes up positions in nearby buildings.

Sahar Mussa, 38, lives on the top floor of an apartment building overlooking the tomb, making it both a potential threat to the worshippers and a useful position for troops, who typically take it over before the buses come in, she said.

The soldiers usually arrive before midnight, move Mussa, her husband and her children into one room and take up posts at the windows until the last worshippers leave, she said.

"They wake us up, pick a place and say, 'Sit here,'" she said. Her door bore circular indentations where she said soldiers pounded with the muzzles of their weapons. The army said it uses "external lookout points," such as rooftops, but does not take over people's homes.

The authenticity of Joseph's Tomb is a matter of debate, though the identification with Joseph is many centuries old. Some local Palestinians say the building was a mosque, or the tomb of a sheik. But that means little to the Jewish worshippers who revere the site.

Israel had a permanent presence at Joseph's Tomb until the outbreak of the Palestinian uprising in 2000, when troops were pulled out after deadly fighting. Palestinians then burned the building.

In 2007, with violence largely subsided and ties improving with Palestinian security forces, the Israeli military began escorting Jews in to pray at the site, where the Oslo peace agreements of the 1990s stated that Jews would have unimpeded access.

Worshippers get about half an hour at the tomb before organizers hurry them out to allow the next buses in. The convoys continue until just before dawn, when all Israeli forces are supposed to be out of the city.

On Monday, hundreds of Israelis who could not find room on the buses defied the army and made their way on foot. Groups of youths in the black suits of religious seminary students were visible around 3 a.m. on West Bank roads, appearing ghostly in the headlights of a passing car.

Fifty worshippers refused to leave the tomb when dawn broke, and with Palestinian residents waking up, the soldiers guarding the worshippers had to forcibly evict them. The military condemned their "irresponsible behavior" and said they had endangered the troops.

Not long afterward, the last Israelis had left. The tomb was quiet, and Nablus reverted to Palestinian control.