BEERSHEBA, Israel, AP -A suicide bomber blew himself up outside a bus station in the southern Israeli city of Beersheba on Sunday, critically wounding two people in the first such attack since Israel began its withdrawal from the Gaza Strip this month.

There was no immediate claim of responsibility. Various Palestinian militant groups have threatened attacks to avenge an Israeli raid in the West Bank last week that killed five Palestinians.

The attack occurred in a dirt parking lot outside the station, which was crowded with morning rush-hour travelers. Witnesses said two security guards halted the bomber, preventing a deadlier attack.

&#34I was suspicious of him. He had a large backpack and a plastic bag in his hand,&#34 a witness who identified himself as a bus driver named Rami told Israel Radio.

&#34I pointed him out to the guard. He was about 20 meters (yards) from the bus when he blew up. It was a huge explosion, very big,&#34 he said.

Yehuda Shoshan, a paramedic, said the two security guards were critically wounded. &#34They were suffering from shrapnel wounds and burns all over their bodies,&#34 he told Channel 10 TV.

At the scene of the attack, the body of the bomber, ripped to pieces by the explosion, lay in the dirt. Nearby, a gray car was splattered with blood and its windows blown out by the force of the blast. Windows on a bus were shattered, and its side was pockmarked with shrapnel.

The bombing was the third since Israel and the Palestinians declared a cease-fire in February, and it rattled efforts to use the Gaza withdrawal as a springboard to resuming peace talks.

&#34Israel has taken the necessary steps to further the prospects of peace with the Palestinians,&#34 said David Baker, an official in the office of Prime Minister Ariel Sharon. &#34This bombing … is another indication that the Palestinian Authority must take proper steps against terror, and without these steps, there will be no progress between both sides.&#34

Israeli authorities suspected the attacker came from the Hebron area in the southern West Bank. Construction of Israel”s massive West Bank separation barrier hasn”t been completed in that area, enabling militants to infiltrate southern Israel relatively easily. Two suicide bombers from Hebron struck Beersheba in August 2004, killing 16 people, prompting Israel to speed up construction in the area.

There has been a lull in violence since the cease-fire declaration last February, but sporadic fighting has persisted. Israel has accused the Palestinians of failing to take tough enough action against militants during the quiet, while Palestinian militants accuse Israel of violating the truce through continued arrest raids.

Five Palestinians, including at least three armed militants, were killed in last week”s raid in the West Bank town of Tulkarem, prompting calls for revenge from Hamas, Islamic Jihad and Al Aqsa Martyrs” Brigades.

Khaled al-Batch, an Islamic Jihad leader in Gaza, said he did not know who carried out the attack. &#34But it came as a natural reaction to the occupation crimes,&#34 he said. &#34It is our right to retaliate.&#34

Palestinian negotiator Saeb Erekat condemned the attack. &#34We … call upon all to make a maximum efforts in order to maintain the truce and quiet,&#34 he said. &#34Violence will bring more violence, and what Israelis and Palestinians need today is more peace and not violence.&#34