GAZA CITY, Gaza Strip — Israel pressed forward with a broad offensive against Islamic militants yesterday, killing an Islamic Jihad commander in an airstrike in the Gaza Strip and rounding up more than 200 wanted Palestinians.

Prime Minister Ariel Sharon promised to use "all means" against the militants, and Hamas later said it would halt rocket fire. Early today, the Israeli military carried out two airstrikes in Gaza.

The offensive, coming just two weeks after Israel withdrew from Gaza, followed a wave of Palestinian rocket attacks against Israeli towns over the weekend. Israel has promised to continue with its airstrikes, arrests and a possible ground invasion until the rocket fire ceases.

"There shall be no restrictions on the use of all means to hit the terrorists and the terror organizations, their equipment and their hideouts," Sharon told his Cabinet yesterday.

Despite the pledge from Hamas, Israeli officials said they would wait to see if things remained quiet before calling off the offensive.

The pullout and the recent wave of fighting have weakened Sharon in his ruling Likud Party ahead of a crucial vote today. Sharon walked out of a stormy Likud meeting yesterday without delivering his prepared speech after what appeared to be an intentional electricity outage prevented him from speaking.

Many party members are angry at Sharon over the pullout, and it appeared that his opponents sabotaged the electric system. Today's vote will set a date for party primaries, and a setback for Sharon could force him to leave the party he founded three decades ago, most likely to form a new centrist party.

Early today, an Israeli helicopter fired a missile in an attack the army said was aimed at a road in Gaza leading to a field used by Palestinians to fire rockets at Israel. In another attack early today, an Israeli helicopter fired two missiles at a workshop the army said was used by Hamas to make weapons.

That airstrike in Gaza City set the building on fire, but no casualties were reported in either attack.

Yesterday's airstrike killed Islamic Jihad's top commander in southern Gaza, Mohammed Khalil, and his bodyguard as they drove along a coastal road in Gaza City.

The airstrike signaled a return to Israel's policy of killing militant leaders, which was halted after a February cease-fire declaration.

The army said Khalil, 35, was responsible for attacks that killed 17 Israelis.

After the airstrike, Mohammed al-Hindi, Islamic Jihad's top leader in Gaza and the West Bank, said the group would no longer honor the cease-fire.

Although the truce has brought a sharp drop in fighting, Islamic Jihad has carried out a series of attacks in recent months, including three suicide bombings in Israel.

Mahmoud Zahar, leader of the much larger Hamas group, said he had ordered an end to rocket attacks and a halt in military-style celebrations in order to preserve the truce.

The latest violence erupted after a blast killed 20 people at Hamas military parade celebrating the Gaza pullout. Hamas blamed Israel, but the Palestinian Authority said the explosion was caused by the mishandling of explosives. Israel, which usually acknowledges attacks on militants, denied involvement.

Hamas responded by firing nearly 40 rockets into Israel, sparking the Israeli offensive.

Early yesterday, Israel arrested 207 wanted Palestinians in the West Bank, most of them members of Hamas and Islamic Jihad.