Jerusalem ? Israeli troops shot and killed two Palestinians who attacked an army post with grenades Saturday, and militant Islamic groups said they would ignore any truce deal, complicating U.S. efforts to arrange a cease-fire.

Amid the ongoing turbulence, U.S. envoy Anthony Zinni planned to mediate another round of cease-fire talks today. Zinni has been meeting with both sides for the past 10 days on a U.S. truce plan that both Israelis and Palestinians have endorsed in principle.

Zinni “shows a serious determination to reach a solution within the coming two days, and we hope he will succeed in doing it,” said Abdel Razak Majaida, the Palestinian chief of public security in the Gaza Strip.

Despite optimistic forecasts, the Israelis and Palestinians disagree on the timetable for carrying out the truce plan, with each insisting the other take the first key steps. And the persistent violence keeps threatening to torpedo the negotiations.

In the northern Gaza Strip, the two Palestinians tossed grenades as they tried to storm a military outpost, but they were shot and killed by Israeli troops, the army said. The attack took place near the Jewish settlement of Dugit.

In the nearby Jebalya refugee camp, mosque loudspeakers said the two men belonged to the militant group Hamas, and were “killed in an honorable fight with the enemy.”

According to Palestinians, a third Palestinian, schoolteacher Subhu Abu Manus, was killed by shrapnel from an Israeli tank shell in Khan Younis in the southern Gaza Strip. Witnesses said the tank fired after stone-throwing by Palestinian youths.

Also in Gaza, a 4-year-old Palestinian girl died, two days after being shot in the head, hospital officials said. Her family said she was playing outside her home in Rafah refugee camp when Israeli troops stationed along the Israeli-Egyptian border fired on the camp.

Meanwhile, Islamic Jihad and Hamas, the two militant Islamic groups that have carried out most of the suicide attacks, said they would not abide by any cease-fire agreement.

Islamic Jihad spiritual leader Sheik Abdullah Shami called on the Palestinian Authority to “stay in the trenches of resistance because there is no way to end the occupation other than struggle.”

Hamas spokesman Ismail Abu Shanab said Israel could not be trusted to observe a cease-fire.

Israel, backed by the United States, has repeatedly called on Palestinian leader Yasser Arafat to clamp down on militant groups.

On Saturday night, President Bush said Arafat has not done enough to fight terrorism.

“There’s been no question that the United States has stood strong with Israel, and we’ve made it clear to Mr. Arafat that he is not doing all he can do to fight off terror,” Bush said at a news conference in Lima, Peru, part of a four-day Latin American tour.