Israeli occupation forces opened fire on the 18-year-old after he threw stones at them near the Askar refugee camp east of Nablus, witnesses said. He sustained light injuries.

Earlier in the day Nablus had been cut off by Israeli troops who formed sand barriers to close the city's northern entrance.

Witnesses said hundreds of Palestinians had been stranded at the Bayzan district in the town, which Israeli bulldozers closed with tall sand barriers, cutting Nablus off from the northern West Bank.

Tunnel find

Hours earlier the Israeli army said it had uncovered a tunnel leading from the northern Gaza Strip into Israel in what was the first such discovery since Israel completed its withdrawal from the territory in September.

The tunnel, which was near the main Erez crossing in northern Gaza, was to have been used by resistance fighters to "infiltrate Israel and carry out terror attacks", the army said.

Palestinian policemen check a
tunnel in May 2005 (File photo)

The tunnel, about 20m long, led under the border to a rubbish dump on the Palestinian side. 

Before their departure from Gaza in September, Israeli forces carried out regular raids inside the southern border town of Rafah to destroy such tunnels.

Last December, a similar tunnel was discovered near the Karni industrial crossing east of Gaza City.

Abbas appeal

Meanwhile, Mahmoud Abbas, the Palestinian president, has told the resistance groups to renew their commitment to a nine-month-old truce with Israel, and a senior US official urged him to step up efforts to disarm them.

"We have agreed one truce, therefore, we should continue with it until security prevails in order that citizens will not feel threatened by [Israeli] planes and tanks," Abbas said.

Abbas and Ariel Sharon, the Israeli prime minister, agreed on a truce in February. Abbas coaxed Hamas and other resistance groups behind the Palestinian uprising against the occupation into honouring the ceasefire until the end of 2005, when Palestinian parliamentary elections are due.

Ongoing fighting

But violence has surged in recent weeks, dashing hopes that talks on a long-stalled US-backed "road map" peace plan would be renewed soon after Israel's pullout from the Gaza Strip, which ended 38 years of occupation. 

A Hamas statement said it would continue to abide by the truce, but that the group would not be barred from carrying out resistance attacks against the Jewish occupation.

Mahmoud Abbas called for renewed
commitment to the truce

Speaking at a ceremony for the laying of a cornerstone for a court building in Gaza, Abbas said the actions of fighters were harming the Palestinian people.

"Security must prevail in this land and all armed displays must end," he said. "Those who are still doing them are working against their people." Abbas also reiterated his earlier call for an end to armed parades and demonstrations.

Welch's comments

David Welch, the US under-secretary of state, on a visit to the region to promote peace talks, reiterated America's call to Abbas to disarm resistance groups.

"In every responsible country in the world the only authority to use force belongs to the government," Welch said.

"This is our expectation of what would happen with the Palestinian Authority, there should be no militias, there should be no terrorist organisations."

Israel says it will not renew negotiations with the Palestinians on a permanent peace accord until Abbas dismantles armed groups. Abbas has preferred to co-opt them.

Tensions have grown especially high since a Palestinian bomber from Islamic Jihad killed five Israelis on Monday. Israel killed three Palestinian fighters in the past week in air raids in Gaza.

Palestinian fighters in northern Gaza have increased their rocket attacks in recent weeks. The al-Aqsa Martyrs Brigades, the armed wing of Abbas's Fatah faction, said on Saturday that its men fired several rockets into Israel. 

David Welch (L) with Palestinian
minister Mohammed Dahlan

Mohammed Dahlan, the Palestinian civil affairs minister, also referred to the security situation, condemning the continued rocket fire into Israel.

"There is no justification for the firing of rockets into Israel," Dahlan said.

"There was no need for these rockets to be fired before the withdrawal and there is no need now." He said the Palestinian Authority was "increasingly worried" about Israel's retaliatory air strikes.

Israel has staged dozens of air raids over the Gaza Strip and has killed a number of Hamas leaders since its withdrawal.

Arrest

Also on Saturday, Israeli police arrested a 20-year-old Palestinian at a checkpoint between Jerusalem and the southern town of Bethlehem who was carrying two small, makeshift explosive devices.

Shmulik Ben Ruby, a spokesman for the Jerusalem police, said the suspect told investigators that he had intended to detonate the devices, described as "similar to fireworks", at the checkpoint in "revenge" for his being injured by army gunfire two years ago.