Israel killed five Hamas gunmen in air strikes on Friday in retaliation for a deadly Palestinian rocket barrage, resuming its assassination policy against militants as a five-month-old truce appeared to be unravelling.
The militant Islamic group Hamas said the back-to-back missile strikes in the West Bank and Gaza Strip would "open the doors of hell" on Israel, and said it was reconsidering its commitment to the cease-fire.
The flare-up of violence, one of the worst since Israel and the Palestinian Authority declared an end to hostilities in February, raised the prospect of disruptions to Israel's planned pullout of settlers from occupied Gaza next month.
The Israeli strikes followed the killing of a young Israeli woman in a rocket attack on Thursday that sparked the fiercest internal fighting in years between militants and Palestinian police, who confronted them trying to stop further salvoes.
Two bystanders were killed and 26 people wounded in the gunbattles, which raised Palestinian fears of civil war, and the Palestinian Authority declared a state of emergency in Gaza.
President Mahmoud Abbas, struggling to salvage the truce and keep control in the face of a growing Hamas challenge, ordered police to act amid Israeli threats of harsh reprisals.
Israel launched a series of air raids against Hamas targets in Gaza before dawn on Friday, causing no casualties.
Hours later, one militant was killed in a helicopter strike on a mountain hideout near the Jewish settlement of Ariel in the occupied West Bank, Palestinian security sources said. They originally reported three Hamas men were killed but later said the other two were either wounded or had escaped.
Within minutes, helicopters over Gaza launched a missile into a car, tearing it apart and killing four militants inside, hospital officials said. Hamas officials said the car was carrying a cache of makeshift Qassam rockets.
The Israel army said it targeted "wanted terrorists" in the West Bank strike and that the Hamas cell hit in Gaza was on the way to carry out rocket attacks.
Israel had reaffirmed its intention to resume what it calls "targeted killings" of top militants following an Islamic Jihad suicide bombing that killed five Israelis on Tuesday. It had suspended the internationally condemned policy under the truce.
The Palestinian Authority said the Israeli strikes would only lead to escalating violence.
Defying Israel's army and Palestinian police, Hamas kept up rocket volleys into southern Israel and mortar fire on Gaza settlements, causing damage but no casualties.
The surge in bloodshed could complicate Israeli Prime Minister Ariel Sharon's plan to withdraw all Jewish settlers from Gaza starting in mid-August, a move international mediators see as a possible springboard to renewed peace talks.