JERUSALEM -- Prime Minister Ariel Sharon of Israel threatened yesterday to freeze peace efforts if the Palestinian leadership does not crack down on militant groups after a weekend suicide bombing in Tel Aviv killed four Israelis and wounded dozens.
At a Cabinet meeting, Israel decided to suspend a plan to turn control of five West Bank towns over to the Palestinians and free 400 more prisoners. Those gestures had been agreed upon at a Feb. 8 summit in Egypt, where Sharon and Palestinian leader Mahmoud Abbas declared a truce.
The attack and the Israeli measures underlined the fragility of the truce and its vulnerability to violence by extremists who oppose any accommodation.
Sharon asserted that Syria was behind the suicide bombing at a Tel Aviv nightspot Friday that killed four Israelis, the first such attack since Abbas took office in January. Syria denied the allegation.
Islamic Jihad, a Palestinian militant group with leadership in Lebanon and Syria, claimed responsibility Saturday after first denying any connection to the bombing.
At the beginning of the weekly Cabinet meeting, Sharon said Islamic Jihad carried out the bombing on orders from its leaders in Syria. ''We know this for certain," he said, although he held the Palestinian Authority responsible as well.
''There will be no progress politically, and I repeat, no political progress, until the Palestinians carry out a determined campaign to destroy the terrorist groups and their infrastructure," Sharon said.
He warned that if this is not done, ''Israel will have to increase its military activities that are meant to protect the citizens of Israel."
A senior military official said on the condition of anonymity that Israel would not hit back for the bombing. The head of the Shin Bet security service, Avi Dichter, said Israel's policy is to pressure Abbas to crack down on the violent groups.
Sharon told US Secretary of State Condoleezza Rice that if Abbas continues to try to control the militants by persuasion, ''terrorism will continue . . . and Israel cannot accept that," a statement from Sharon's office said.
Rice had called to offer condolences over the bombing, it said. Sharon said talks on the US-backed ''road map" peace plan could not begin unless there were ''active steps against terrorism."
Palestinian Prime Minister Ahmed Qurei dismissed Sharon's warnings.
''If Israel wants to cut off contacts with the Palestinians, it will be its own decision and we will not cry," Qurei said. ''But we say that there is an opportunity begun in Sharm el-Sheik, and we want to develop this effort," referring to the summit where the truce was declared.
Relations between Israel and the Palestinians have warmed considerably since Abbas's election last month.
Abbas has deployed Palestinian security forces throughout the Gaza Strip to prevent militants from firing rockets on Israel, and brokered a temporary agreement with the militant groups to halt attacks. In response, Israel released 500 Palestinian prisoners, promised to end the killings of militant leaders, and agreed to hand over security control of five West Bank towns to the Palestinians.
After Friday's attack, Israel froze plans for the security handover because it said it no longer believes the Palestinian security forces are capable of controlling the towns. Qurei criticized the decision as ''wrong and unacceptable." Israel also put on hold the release of 400 more prisoners, Cabinet Minister Tzipi Livni said, adding that their release was contingent on Palestinian moves to halt violence.
Meanwhile, Foreign Minister Silvan Shalom of Israel summoned ambassadors from the European Union and UN Security Council members to a meeting today, where he said military intelligence would display proof of Syrian involvement in the Tel Aviv bombing. The Foreign Ministry said it would not make the proof public. Foreign Minister Farouk al-Sharaa of Syria denied his country was involved in the attack.
Vice Premier Shimon Peres of Israel said President Bashar Assad of Syria was responsible because the orders came from his country.
''He has to decide which world he belongs to -- the world of terrorism or the world that fights terrorism," Peres told Army Radio.