Defiant Palestinian militants pounded Jewish settlements in the southern Gaza Strip (search) with mortar fire Friday, following the killing of a top Hamas (search) militant in an Israeli airstrike.

The Islamic militant group threatened attacks on Israel to avenge Adnan al-Ghoul (search), a founder and deputy chief of the Hamas military wing. A lower-ranking militant was also killed in the airstrike Thursday night.

Al-Ghoul, 46, was a top bombmaker and was responsible for Hamas' weaponry, including anti-tank missiles and Qassam rockets the group has been firing at Israeli communities, the Israeli army said. Held responsible for the deaths of dozens of Israelis, he had escaped previous attempts on his life.

Following the killing of al-Ghoul, around 15 mortar rounds were fired at the Jewish settlement of Neve Dekalim and adjacent military posts, damaging four houses but causing no casualties. Settlers reported mortar shells falling on two other south Gaza settlements, but causing no damage.

One militant was killed and another gravely injured as they prepared to fire a mortar at Neve Dekalim, Palestinians and the army said. Palestinians said the dead man was a known Hamas activist. It was not immediately clear if the men were hit by Israeli fire or whether the mortar shell exploded prematurely.

Al-Ghoul's death dealt a tough blow to Hamas, which is responsible for the deaths of hundreds of Israelis during four years of fighting.

"Hamas retaliation will be painful and the Zionist enemy will regret this awful crime," said Hamas spokesman Mushir al-Masri, surrounded by hundreds of supporters outside the morgue where al-Ghoul's body was taken.

Al-Ghoul had been in hiding for years, avoiding public appearances and media interviews.

Upon news of al-Ghoul's death, thousands of angry Hamas supporters took to the streets in several Gaza refugee camps, calling for revenge and chanting anti-Israel slogans.

However, Hamas' ability to strike back at Israel has been severely weakened by a string of assassinations.

Early this year, Israel killed the group's spiritual leader, Sheik Ahmed Yassin, and his successor, Abdel Aziz Rantisi.

A top Hamas leader based in Damascus, Syria, was killed in a car bombing last month. Israeli security officials acknowledged involvement. Most Hamas leaders in Gaza have gone into hiding.

Al-Ghoul's killing leaves the Hamas military leadership solely in the hands of Mohammed Deif, its longtime chief. Deif, like al-Ghoul, is high on Israel's wanted list and has been in hiding for years. They both escaped a September 2003 airstrike aimed at a gathering of Hamas leaders in Gaza.

Palestinian Cabinet minister Saeb Erekat condemned Thursday's killing, which he said "reflects the determination of the Israeli government to continue the path of military solutions rather than negotiations."

Later Thursday, an Israeli helicopter fired a missile in the northern Gaza Strip, causing no injuries but destroying the home of a local militant leader, witnesses said. The army said it destroyed a weapons workshop.

In the southern Gaza Strip, Israeli tanks and bulldozers moved about 100 yards into the Rafah refugee camp early Friday, witnesses said.

An Israeli helicopter hovered overhead, firing bursts of gunfire, and Palestinian gunmen returned fire. Israeli military sources confirmed an operation was under way, but declined to give details.

The Rafah camp, located on the Egyptian border, is a flashpoint of violence, and an Israeli soldier was killed in the area on Thursday.

Gaza has experienced an upsurge in violence since Prime Minister Ariel Sharon announced plans earlier this year to withdraw from the volatile area. Both Israel and militants want to claim victory ahead of the withdrawal.

Sharon is planning to present his Gaza withdrawal plan to the Israeli parliament for a vote of approval on Tuesday.

Aides to the prime minister said Thursday that he has locked up enough support to win that vote, but is deeply concerned about growing fissures within the ruling Likud Party over the plan.

Just over half of Likud's 40 lawmakers are expected to support Sharon, meaning he will have to rely on moderate opposition parties to prevail.

Sharon says a continued presence in Gaza, where 8,200 Jewish settlers live among 1.3 million Palestinians, is untenable. The plan also includes a pullback from four small West Bank settlements.

Tuesday's vote is only the first of three parliamentary votes on the plan. A victory would give him strong momentum as he pushes forward, although the government could still fall on other issues, including the budget, before the planned withdrawal begins next summer.