Israel security forces today placed a curfew on the West Bank city of Hebron and sealed off the nearby Kirvat Arba Jewish settlement after a Jewish religious student was shot to death while walking through an Arab open-air market.

The shooting increased tensions in Kiryat Arba as some activists of the Ultranationalist Gush Emunim settlement movement and the militant Jewish Defense League bitterly complained that the Arab police in Hebron left the victim lying in the marketplace while other Jewish settlers pleaded for help.

After some Kiryat Arba residents threatened revenge, security forces sealed off the sprowling, 500-family settlement that sits on the outskirts of the Arab city.

"They [the Kiryat Arba residents] said they are not going to sit quiet, so we closed the gate. Nobody can go out or in. We don't want something worse to happen," said a spokesman for the West Bank military government.

Authorities said the religious student, 20, whose name was withheld pending notification of relatives, was shot twice in the head at close range. Authorities said they had no motive or suspects in the death.

The first indication of the attack, which occurred in Hebron's teeming open-air food market in the center of the city, came when two women from Kiryat Arba noticed that Arab merchants suddenly began shuttering their stalls and the streets began emptying, police said. The women said they began asking what had happened, but were told nothing until they found the student lying in a pool of blood.

They told investigators they cried for help but the local Arab policemen who patrol the market had left. An Israeli police patrol arrived and took the youth to a local Arab hospital from which he was taken by helicopter to the Hadassa Hospital in Jerusalem.

The youth died tonight at the hospital following emergency surgery. He was a member of the Israeli Army, but he was not in uniform at the time of his death.

The shooting was the latest -- and most serious -- of a series of clashes between Jewish civilian settlers and Arab residents of Hebron.

Israeli Army Brig. Gen. Benjamin Ben-Eliezer, commander of the West Bank military government, and other top security officials went to Kiryat Arba to talk with residents and attempt to reduce tensions.

Friction between the two communities has increased because military authorities have fenced off a tract of land adjacent to Kiryat Arba for expansion of the settlement. Palestinian leaders say the land is Arab-owned and that the seizure is illegal.

Hebron Mayor Fahd Kawasma and Mohammed Milhem, mayor of the nearby town of Halhoul, were arrested earlier this month on charges of incitement when they led a protest against construction of the new housing project.

Last June, several Arab Hebron residents complained their homes were broken into and that they were beaten by Israeli settlers who claimed the houses had been Jewish-owned beforethe 1929 Hebron riots, in which a number of Jews were killed.

Two members of Rabbi Meir Kahane's Jewish Defense League were arrested in connection with those attacks. A month earlier, Kiryat Arba residents were accused of uprooting Arab vineyards near the settlement.