JERUSALEM (AFP) - Police on Sunday caught four young Israelis red-handed as they vandalised Christian tombstones in a cemetery in the holy city of Jerusalem, a spokesman said.

"Four Israeli Jews aged between 17 and 26, including two from settlements in the West Bank, were arrested as they broke tombstones in a Christian cemetery on Mount Sion," spokesman Micky Rosenfeld told AFP.

He said 15 tombstones were vandalised in the graveyard near the Old City.

Spokesman Rosenfeld said police were pursuing two lines of inquiry - that the attack was "a criminal incident motivated by nationalism" or that it was a "hate crime".

In July, two suspects were arrested after vandals set fire to the door of a Trappist monastery in Latrun, 15km from Jerusalem, in September last year.

Attackers had scrawled "Jesus is a monkey" on a nearby wall in an incident that shocked the religious and political establishment.

The Trappist abbey lies just inside the West Bank, very close to the 1949 armistice line, and is one of the most famous monastic sites in the Holy Land.

One suspect in the attack was from the Beit El settlement, north of the Palestinian political capital of Ramallah.

Extremists from settler and far-right groups often launch so-called "price tag" hate crimes against Palestinian and Israeli Arab villages.

Muslim and Christian sites, Israeli pacifists and even the military have also been targeted in reprisal for government decisions deemed hostile to their interests.