The incident on Saturday in the Rafah refugee camp, located along the border with Egypt, shattered weeks of calm and added to tensions surrounding plans by Jewish radicals to march on a disputed holy site in Jerusalem.

Ali Abu Zaid, a 22-year-old Rafah resident, said a group of boys were playing football in an open area when the ball was kicked towards the border fence. "The kids ran after it, and that's when we heard gunfire," he said. Palestinian hospital officials earlier said two of the dead youths were 14 and 15 years old.

The Israeli army said a group of youths had entered an unauthorised area near the border and ignored warning shots to stop. The shots were fired by forces patrolling the area in an armed vehicle, the army said.

The Rafah refugee camp has been a frequent flashpoint of fighting since violence broke out in late 2000. The Israeli army frequently operates in the area to halt weapons smuggling across the border.

But violence has dramatically dropped since Israeli Prime Minister Ariel Sharon and Palestinian leader Mahmud Abbas declared a cease-fire on 8 February.

Deadly attack

Since the 8 February declaration, a total of 13 Palestinians have been killed in clashes with Israel. But Saturday's shooting was the deadliest single incident. Five Israelis have also died during the period, all killed in a 25 February bombing outside a Tel Aviv nightspot.

Hamas pledged to avenge the
deaths of the three teens

The chief Palestinian peace negotiator, Saib Uraiqat, said the shooting threatens peace prospects. "Every time we have such a violation of the cease-fire it really endangers the fragile quiet," he said. "We urge the Israeli government to refrain from any acts that could endanger the ceasefire."

Hamas, the largest Palestinian resistance group, pledged to avenge the deaths of the three teens. "The Palestinian people cannot stay silent in the face of this crime and it cannot pass without punishment," said Said Siyam, a Hamas leader in Gaza.

He would not comment on whether Hamas remained committed to the truce. Muhammad al-Hindi, leader of the Islamic Jihad resistance group, called the shooting an "ugly crime" and said the Palestinians would have to re-evaluate the ceasefire.

But he too declined to say whether the truce would be called off. Shortly after the shooting, Palestinians fired five mortar shells towards Jewish settlements in Gaza, causing no injuries, the army said.