Tensions between Palestine and Israel escalated as an Israeli airstrike on northern Gaza killed at least seven people on Thursday.

The raid came hours after Israeli Prime Minister Ariel Sharon vowed a broad offensive in retaliation for an Islamic Jihad (Holy War) suicide bombing that claimed five lives in Israel's northern town of Hadera on Wednesday.

Shadi Mohanna, the field commander of Islamic Jihad in the northern Gaza Strip, along with his assistant, Mohammed Ghazaineh, were among the dead, said security and medical sources.

Palestinian security sources said the two were members of Saraya al-Quds, the armed wing of Islamic Jihad.

Israeli missiles hit their car, a white Subaru, when they were driving just outside the Jabalia refugee camp, said witnesses.

They added that Israeli helicopters hovered over northern Gaza and fired at least two missiles, which caused powerful explosions. The other five killed were civilian bystanders.

Palestinian Ministry of Health declared Thursday night a state of emergency in all its hospitals after the strike.

Moweya Hassanein, chief of emergency in the ministry, said in a press release that the ministry called on all its medical staff and rescue teams in hospitals to stand alert.

Dozens of Palestinian children and pregnant women were admitted at hospitals due to the airstrikes, said Hassanein.

Islamic Jihad declared revenge immediately after the attack. "The war with Israel is now opened," it said.

As hatred stirred up by the attack was still boiling in Palestine, Israel lost no time in launching a second strike later Thursday on northern Gaza.

There were no immediate reports of casualties in the second explosion, said Palestinian security sources, adding the target of the latest bombardment was an open field used by militants to launch rockets into southern Israel.

Palestinian chief negotiator Saeb Erekat warned Israel on Thursday that the Jewish state's harsh response to a suicide attack threatened to send an eight-month-old ceasefire into collapse.

"The Israeli moves might bring a total collapse for the current calmness and more bloodsheds," he said.

Urging both Israel and Palestinians to exercise restraints, the senior official also called upon the Quartet Committee, which groups key Mideast peace mediators -- the United States, the European Union, the United Nations and Russia, to immediately intervene in a bid to save the ceasefire deal.

The virulent development has drawn immediate responses from Washington. US Secretary of State Condoleezza Rice called Palestinian President Mahmud Abbas on Thursday, urging him to rein in militants.

"She encouraged the Palestinian Authority, President Abbas, to act to stop terror attacks as well as ... to start dismantling those terrorist networks that are responsible for these acts of terror," State Department spokesman Sean McCormack told reporters.

Under current circumstances, Israeli Prime Minister Ariel Sharon ruled out talks with Abbas, saying the meeting is out of question until he takes "serious action" against armed groups.

Source: Xinhua