Israeli troops killed a Palestinian Friday after militants fired missiles at a Jewish settlement in the Gaza Strip (search) in the third consecutive day of violence hampering efforts to salvage a shaky truce.

The army said three militants fired missiles, mortars and assault rifles from an abandoned building near the Gaza settlement of Kfar Darom (search). One of the militants was killed in an ensuing gunbattle with troops while two others escaped.

Israel threatened harsh retaliation for the latest attacks and warned a cease-fire reached in February at the Egyptian Red Sea resort of Sharm el-Sheik was in danger of collapse.

The Islamic group Hamas (search) said it carried out the attack jointly with the Al Aqsa Martyrs' Brigades (search) — a militant group linked to Palestinian leader Mahmoud Abbas' (search) ruling Fatah party — and the Gaza-based Popular Resistance Committees. Hamas said the attack was in retaliation for Israeli strikes.

The past three days of fighting has erupted while Abbas is on a two-week tour of South America and Asia, prompting Israeli criticism not only of the violence but also of his lengthy absence.

The ongoing violence "only shows that their leader has to be in the area and not disappear for 20 days," said Asaf Shariv, an adviser to Prime Minister Ariel Sharon (search). "We sent very strong messages that the Sharm understandings are in great danger and if the Palestinians don't stop the firing then we will have to do it."

A senior Israeli military official, speaking on condition of anonymity, said Hamas has been ratcheting up violence in an effort to strengthen itself ahead of a showdown against the ruling Fatah party in Palestinian parliamentary elections, scheduled for mid-July.

The failure of Palestinian police to stop the militants before they carry out the attacks underscored the challenges Abbas faces in trying to curb militants and keep peacemaking on track.

Renewed violence could complicate Israel's planned pullout from Gaza and four West Bank settlements this summer. The United States and Europe hope the pullout will be a stepping stone for the resumption of long-stalled peace talks.

Israeli and Palestinian negotiators met Thursday in an attempt to defuse the situation, with Israel agreeing to move ahead on a promised Palestinian prisoner release.

In New Delhi on Friday, Abbas expressed hope the truce would hold.

"I hope that all the parties will stick to the truce and they will not escalate (violence)," Abbas said. "Some incidents are taking place here and there, but I hope that we can contain and control all these incidents because the truce is in our interest and in the Israeli interest. So we have to preserve it."

After the Gaza attack, about 100 Kfar Darom settlers, some armed, marched toward the abandoned building where the militants staged their assault to set up a defensive position there. Israeli soldiers ordered them to turn back, and they had a brief scuffle.

The army, meanwhile closed Gaza's main cargo crossing, citing security concerns.

Israeli-Palestinian clashes have dropped sharply since the truce, which aimed to end more than four years of conflict.

But violence has erupted sporadically, with the latest round starting Wednesday. Over the past three days, three Palestinians have been killed, and Palestinian militants have fired dozens of missiles, rockets and mortar shells at Jewish settlements in Gaza and at Israel.

On Thursday, Israeli Defense Minister Shaul Mofaz called military commanders in for consultations and let it be known that Israel would go back to targeting militants about to launch attacks — as it did Wednesday, killing a Hamas militant in Israel's first air strike since the truce.

Still Hamas leader Mahmoud Zahar said the group's informal truce with Israel remained in effect though he added: "We are committed to defend ourselves in the face of any (Israeli) aggression in the West Bank and Gaza."

Mofaz said during a closed meeting with security chiefs that Palestinian police were not fulfilling their obligations to stop the militants. Mofaz said he would not allow Israelis to be harmed and would exact a price for attacks by militants, meeting participants said.

Security officials said Mofaz plans to bring a list of 400 Palestinian prisoners to be freed before the Cabinet on May 29 — an apparent bid to shore up Abbas as he tries to restore order and heads into elections. Israel pledged to free the prisoners as part of the truce but stopped the process, accusing the Palestinians of not holding up their end of the deal.