Israeli officials said Wednesday that the military would begin targeting for assassination members of Islamic Jihad who were planning attacks against Israel, a move that Palestinian officials warned could destroy a truce that has reduced violence since it took hold four months ago.

Israeli officials said the policy, developed over the past two days, did not mean a return to the assassinations it once carried out against members of armed Palestinian groups. Such killings were suspended in February after Prime Minster Ariel Sharon and Palestinian Authority President Mahmoud Abbas agreed to a temporary truce.

Instead, Israeli officials said, military forces would target Islamic Jihad members actively planning attacks against Israel. Islamic Jihad fighters have killed one Israeli soldier in the Gaza Strip and an Israeli settler in the West Bank over the past four days, spurring the arrest of 52 of its members by the Israeli army. Israeli officials said Wednesday that a missile strike on Tuesday in northern Gaza was an attempt to kill a specific Islamic Jihad member.

Raanan Gissin, a spokesman for Sharon, said Israel's strategy remained within the bounds of the February agreement reached in the Egyptian resort of Sharm el-Sheikh. He said the terms of the truce allowed Israel to defend itself against imminent attack if Palestinian security forces failed to do so, an argument Palestinian officials rejected.

The deteriorating security situation dominated a tense meeting Tuesday in Jerusalem between Sharon and Abbas. The Israeli leader warned Abbas that he would send Israeli forces against armed Palestinian groups if Abbas did not rein them in before Israel began a planned withdrawal from Gaza and four West Bank settlements in mid-August. Abbas has been struggling to consolidate a variety of Palestinian security agencies under one department.

"We're trying to send a very clear message, and the prime minister sent it in clear terms during the summit -- if you don't do it, we'll do it," Gissin said. "The disengagement process is so tenuous and so fragile that one match could blow up the whole thing. What we're imploring them to do is to take action, stop these people, then we wouldn't have to."

But Palestinian officials condemned Israel's decision to strike Islamic Jihad fighters as a violation of the truce, saying the agreement prohibits Israeli military action against Palestinians. Saeb Erekat, the Palestinians' chief negotiator with Israel, said, "This is exactly the wrong road for Israel to take."

"I believe sustaining and maintaining the cessation of violence is to the advantage of Palestinians and Israelis," Erekat said. "This may lead to the collapse of the attempts to revive the peace process. Bullets will lead to more bullets."

Islamic Jihad has roots in the Muslim Brotherhood, a large and influential Islamic group, and was founded not long after the 1979 Iranian revolution, from which it drew inspiration. The group, committed to the creation of an Islamic state and the destruction of Israel, rejects the 1993 Oslo peace accords with Israel that led to an elected Palestinian government in parts of the occupied territories. It has asserted responsibility for a number of suicide bombing attacks against Israeli targets and is designated a terrorist group by the United States. Until recently, however, it had largely abided by the terms of the cease-fire it formally joined in March at Abbas's urging.

Israeli officials say the group is seeking to disrupt Sharon's disengagement plan, which senior government officials warned Wednesday would be defended with as much military force as necessary. Foreign Minister Silvan Shalom said in a statement, "If needed, Israel will return to the Gaza Strip after the disengagement for several days in order to put an end to terror."

Late Wednesday, Israeli military aircraft fired two missiles into the northern Gaza town of Beit Lahiya, targeting a group of Palestinians that witnesses said were preparing to fire rockets. No one was injured.

In an interview with Army Radio on Wednesday, Gideon Ezra, Israel's minister of public security, said that "an opportunity had presented itself" Tuesday evening before an Israeli airstrike in northern Gaza.

"There was an attempt in Gaza to intercept an activist yesterday," Ezra said. "It was unsuccessful. Any means to neutralize the organization are relevant and possible."

Palestinians march in support of Islamic Jihad, an extremist group that has killed two Israelis in four days, threatening the stability of a cease-fire.