A Catholic church at a revered site near the Sea of Galilee in northern Israel was damaged by fire early today, in what the police are treating as an arson attack and possible hate crime.

Graffiti denouncing idol worship using the language of a Hebrew prayer was found spray-painted in red on an outside wall of the church, strengthening the suspicion that Jewish extremists may have been responsible for the attack.

The church, known as the Church of the Multiplication, stands on the site where many Christians believe Jesus performed one of the best-knownmiracles in the Bible, feeding 5,000 people with two fish and five loaves of bread. Pilgrims have visited and prayed at the site for decades.

The fire in the church compound at Tabgha, on the northwestern shore of the Sea of Galilee, broke out shortly after 3am Images distributed by the police showed a stone-walled structure in the compound smoldering with its roof gutted. Firefighters extinguished the blaze before it reached the main prayer hall, and the church's ancient mosaic floors, dating from the fifth century and rediscovered by archaeologists in the 1930s, were unharmed, the police said.

Even so, the damage to the compound was severe, said Micky Rosenfeld, a spokesman for the Israeli police, adding that evidence found at the scene indicated that the fire was set deliberately.

The police briefly detained a group of 16 Israeli youths who had spent the night in the area, several of them from a Jewish religious seminary in Yitzhar, a West Bank settlement known for radicalism. But the youths were soon released because of a lack of sufficient evidence. Mr Rosenfeld said the investigation was continuing.

Israeli leaders condemned the attack. "Such terrible desecration of an ancient and holy place of prayer is an attack on the very fabric of life in our country, where people of different faiths seek to live together in harmony and mutual tolerance and respect," President Reuven Rivlin told the Rev. Gregory Collins, the leader of the Order of St. Benedict in Israel, which runs the church, according to a statement from Mr Rivlin's office.

Gilad Erdan, the minister for public security, described the arson attack as "a despicable, cowardly act that is contrary to the most fundamental values of the state of Israel."

One of the monks assigned to the church, the Rev. Matthias Carl Benedictina, said there had been more than 50 attacks against Christian institutions in Israel over the last three years, including damage to cars and cemeteries. "There is somebody, or a group of extremists - a small group, but an active group - who work against Christian people," he told Israel Radio.

Mosques in Palestinian villages in the West Bank have also been the target of arson attacks by Jewish extremists in recent years.

Few of the cases have led to indictments or convictions, leading Christian and Muslim representatives to question the Israeli authorities' commitment to catching the perpetrators. Israeli security officials say they have difficulty amassing evidence that will hold up in court because the suspects they interrogate rarely talk and because the crimes often require little more than a screwdriver, some gasoline or a can of spray paint.