Mahfuz Abu al Nasr, a Palestinian farmer from the West Bank village of Salem, was grieving yesterday over the wreckage of his livelihood. Jewish settlers had come in the night and destroyed 30 olive trees he planted a decade ago, in revenge for the deaths of three young Israelis in a drive-by shooting last Sunday.

"It is like losing your son," said Mr Nasr, 65, who has 10 children. "I watched them grow every year. At last they were producing. Every tree was as big as a house."

The trees lay scattered on the rocky ground, cut down by power saws. The crushed branches still bore olives ripe for harvest. Only seven trees on his two-acre plot had survived. "I have no shop, no sheep, no cows," he said sadly. "I only had my olive trees."

This was not the first time that militant settlers, waging a war of attrition against their neighbours in the hills east of Nablus for the past four years, had raided his grove.

Every year, their attacks cost Mr Nasr 5,000kg of olives and 180 litres of oil. He is going to plant new trees, but he will have to wait years until they bear fruit. This time, the vengeful settlers had lopped and burned trees on 70 Salem farms.

Adli Ishtiyeh, head of the village council, rushed to the area with 20 others. Palestinian firefighters from Nablus were trying to put out the blaze, but they arrived too late. "The hissing flames were eating our trees," he said. "I saw large boxes of Israeli-made incendiary material on the ground. There were seven or eight settlers."

Mr Ishtiyeh, who lost 70 trees, submitted testimony to Israeli army and police officers, who came to assess the damage. "They asked me if I could identify the perpetrators," he said. "But I can't. I saw them from a distance, watching the flames."

Inspector Michael Rosenfeld, a police spokesman, said: "We see this kind of act as a very serious crime. We intend to investigate it in the same way that we would investigate a Palestinian attack on Jews. We're putting a lot of emphasis on intelligence-gathering." An army officer added: "We want to stop this kind of vandalism once and for all."

The villagers remain sceptical. "The government is not serious," Mr Ishtiyeh said. "This is the sixth time over the years that we have filed complaints, but nothing ever happened."

Arik Ascherman, the director of Rabbis for Human Rights, which has campaigned for the olive farmers, said the security services were trying harder this autumn to enable them to harvest their crop, but said they lacked a coherent plan, and the backing of the courts.

"We have seen an improvement in preventive activity and even a high number of arrests," he said. "But when it goes into the judicial system everything falls apart."