ROSH HAAYIN, Israel - Fracturing an already shaky 6-week-old cease-fire, two teen-age Palestinian suicide bombers blew themselves up in successive attacks yesterday, killing two Israelis and wounding 11 others.

The bombings, at a mall in this small town near Tel Aviv and at a bus stop near the Jewish settlement of Ariel in the West Bank, further threaten a U.S.-backed peace plan already battered as each side accuses the other of failing to make necessary concessions.

The violence also raises the possibility that senior U.S. officials, who have been visiting frequently to coax both sides to agree to the smallest details, will have to become more deeply involved if the peace effort is to be preserved.

Two militant groups, Hamas and the Aqsa Martyrs Brigades, claimed responsibility for the blasts, which came after more than a month of relative quiet. The attacks jolted Israelis back to a time when suicide bombings were a routine part of the Palestinian uprising, raising fears that the short, welcome respite was over.

In Rosh Haayin, municipal worker Shlomo Bashari stood stunned, with blood from a woman he had dragged out of the wreckage smeared on the breast pocket of his blue uniform. "She yelled, 'Save me,'" he said, as rescuers performed the grim and all-too-familiar task of collecting human remains.

Israeli police called the timing of the attacks a coincidence, even though the bombers, both 17, lived a few blocks from each other in the West Bank city of Nablus and died in self-triggered explosions that came only a few miles and less than an hour apart.

A renegade faction of the Aqsa Martyrs Brigades said it sent its attacker to the mall in Rosh Haayin, along the West Bank, where a 42-year-old man was killed inside a supermarket. The faction has refused to honor the cease-fire even though the group is affiliated with Yasser Arafat's Fatah political party, which signed it.

Hamas, which until yesterday had stuck to the truce, said it dispatched its bomber to the bus stop in the West Bank, where an 18-year-old army recruit was killed, to avenge the death of two of its members during an Israeli army raid in Nablus last week.

Hamas gave the Associated Press a letter from the bomber, Islam Yousef Qteishat, saying: "Father, don't be sad, lift your head in pride, because your son died a martyr for the sake of God."

U.S. response

Speaking in Washington, U.S. Secretary of State Colin L. Powell said that the bombings were done "by people who were doing everything they can to destroy the dreams of Israelis and Palestinians alike."

Powell dismissed reports that the peace initiative has failed. "We've already seen reports on television that say, well, the road map is now finished, or the cease-fire is over, or this is all off track," he said. "No, it's not. We cannot let it go off track."

White House officials said the Palestinians "must act now" to dismantle militant groups.

Israel's response was muted as it canceled the release of about 70 Palestinian prisoners, all of them petty criminals; moved tanks closer to Nablus, and imposed curfews on surrounding villages. Government officials said they would act with restraint and preserve the peace process.

Prime Minister Ariel Sharon, visiting the agricultural ministry, said again that the Palestinians had not yet taken security seriously. He did not convene his security Cabinet, which usually meets before large-scale military operations are launched.

"We see that the Palestinian Authority isn't doing what it has to do, and the main thing it has to do is dismantle terrorist organizations, confiscate their weapons and wage an uncompromising campaign against terror," Sharon said. He vowed that the political process would end if "terror does not stop."

Israeli officials were not a party to the three-month cease-fire, which expires at the end of September, regarding it as an internal agreement among the Palestinian Authority and various armed militant factions. Israeli officials have since accused Hamas and Islamic Jihad of exploiting the truce to rearm.

A day after the truce was announced at the end of June, the Israeli army pulled troops back from occupied areas of the Gaza Strip and out of the West Bank city of Bethlehem, and returned security control there to the Palestinians. Since then, five Israelis and one foreign national have been killed in sporadic attacks, most in or near areas still occupied by the Israeli army.

The army has continued to conduct raids, impose curfews and shoot suspected militants in six Palestinian cities on the West Bank still under its control. Army and police officials said they have arrested 10 suicide bombers on the way to attacks since the end of June.