Israel killed two Palestinian militant leaders on Friday in an air strike on a car in the Gaza Strip, the Israeli military and officials in Gaza said.

A third man was also injured in the attack that came shortly after two rockets were fired at Israel from the coastal territory, causing no damage or injury.

At least two men were inside the vehicle, a small metallic blue car, when the air strike hit, witnesses said. Reuters television footage showed one charred body being carried away from the scene.

The Israeli military said in a statement one of the dead was Zuheir al-Qessi, who Palestinians said headed the Popular Resistance Committees (PRC), an umbrella group of armed activists from different factions.

The military said the militants were preparing to attack Israel across the Egyptian border in the coming days, suggesting that the air attack on the car was ordered to stop the planned assault.

The PRC has claimed responsibility for a series of rocket strikes on Israel and said last month the attacks were in response to what it said were threats by Jewish extremists against the al-Aqsa mosque in Jerusalem.

Qessi's death brought a swift call for retaliation from the PRC, threatening to reignite tensions along the testy frontier.

All options are open before the fighters to respond to this despicable crime. The assassination of our chief will not end our resistance, Abu Attiya, a spokesman for the PRC group said.

Fawzi Barhoum, spokesman for the Hamas Islamist government in Gaza, said Israel was responsible for what he called a grave escalation.

They want us to sink in darkness and in blood, he added.

The second man killed, Mahmoud al-Hanani, was identified in Gaza as a local militant leader, originally from the West Bank.

A Hamas official said Hanani had been exiled by Israel five years ago, denying earlier reports he had been one of those freed from an Israeli jail last year as part of a prisoner swap deal to gain the release of Israeli soldier Gilad Shalit.

Qessi was elected chief of the PRC last August after Israel killed his predecessor in an air strike in the southern Gazan town of Rafah.

Israel launched that raid after accusing the PRC of staging attacks along its border with Egypt that killed seven Israelis. The PRC has denied involvement in that cross-border attack, but Israeli charged that Qessi was one of those involved in its planning.

Israel often launches retaliatory attacks after missiles are fired at its territory from Gaza though such strikes had grown rarer in past weeks.

The last lethal Israeli strike in Gaza was in mid-January when two Palestinians were killed in attacks Israel said targeted a squad planting bombs at the border fence.

(Reporting by Nidal al-Mughrabi; Writing by Allyn Fisher-Ilan; Editing by Andrew Heavens)