A Palestinian suicide bomber has injured at least four people after blowing himself up at a crossing point on the border between Gaza and Israel. The bombing on Saturday was the first such attack since President Bush endorsed an Israeli plan to withdraw troops and Jewish settlements from the territory.

The blast on the Israeli side of the Erez checkpoint in northern Gaza shook the entrance to an industrial complex inside the crossing.

The explosion came as the bomber was leaving the industrial area, where about 6,000 Palestinians are employed in factories.

The explosion ripped away part of the corrugated tin roof of the terminal used for security checks on Palestinian workers as they enter and leave the area.

It was the fourth attack on the crossing this year. In March, six Palestinians died in a failed attempt to kill Israeli soldiers. In January, a woman suicide bomber killed four Israelis at Erez.

Following the blast on Saturday, Israeli forces sealed off the area, as military helicopters searched for suspects who might have helped carry out the attack.

Hamas, a group that frequently carries out suicide bombings, claimed joint responsibility with the Al-Aqsa Martyrs' Brigades, an armed wing of Palestinian President Yasser Arafat's Fatah faction.

On Friday, a member of the Islamic Jihad was killed, and two others were injured in an explosion in the West Bank, as they were preparing explosives for an attack against Israelis.

All three groups are listed by the U.S. State Department as terrorist organizations.

The latest violence comes amid increased political tensions, following a summit in Washington this week between President Bush and Israeli Prime Minister Ariel Sharon.

The Palestinian leadership warned that Mr. Bush's statements, which they argue are biased in favor of Israel, would lead to more bloodshed in the region.