JERUSALEM — An Israeli airstrike on Wednesday killed four Palestinian militants near the eastern edge of the Gaza Strip. The Israeli military said that the Palestinians' car was packed with explosives and that they were on the way to carry out an attack.

On the political scene, Palestinian parliamentary elections planned for next month became increasingly tangled Wednesday when rebels from the governing Fatah Party announced that they were forming a new movement.

Fatah, the party of the Palestinian leader, Mahmoud Abbas, is favored in the polls. But a younger generation of Fatah leaders felt they were being denied the chance to advance and presented their own list of candidates.

The rebel faction will be led by Marwan Barghouti, even though he is in an Israeli prison, convicted last year of organizing five killings. His imprisonment appears to have made him even more popular among young Fatah supporters.

The attack was the third lethal air strike in Gaza since a Palestinian suicide bombing on Dec. 5 in Netanya that killed five Israelis. Israel's defense minister, Shaul Mofaz, said the response to the suicide bombing and to the threat of future attacks would be harsh.

The military said that one of those killed was Hamdan Mahana and that he worked at Karni and had gathered information to plan an attack there.

The crossing is used for goods going in and out of Gaza. An agreement brokered last month by Secretary of State Condoleezza Rice called for Karni to be kept open on an "urgent basis." The Palestinians are now harvesting fruit and vegetables, which are among their most profitable exports, and the produce is sent through Karni to Israel, Europe and Arab countries.

Wednesday's airstrike produced a powerful explosion, Palestinian witnesses said. The military said the blast was amplified because the explosives the militants were carrying detonated.

Several Palestinians were wounded, medical workers said. At the Gaza City hospital, where the dead and wounded were brought, an angry crowd gathered outside, chanting, "Destroy Israel!"

Several hours after the first airstrike, the Israeli air force fired a missile at a leader of Islamic Jihad as he was getting in his car in Gaza City. But the man, Khader Habib, apparently heard the aircraft and began to flee. He was among four people wounded, medical workers said.

In politics, the friction within Fatah was again on display. Two groups of Fatah gunmen waged a shootout at the party's Gaza headquarters, wounding three people.

One side was demanding jobs, and was eventually driven away by a second group of armed Fatah men.

In a related development, Palestinian election offices also reopened, a day after Fatah gunmen stormed four offices in Gaza and the West Bank and forced them to close.