Palestinian militants vowed today to avenge Israel's assassination of the Hamas government's top security chief, an attack that threatened to ignite large-scale violence between the two sides.

The security chief, Jamal Abu Samhadana, was a key player in ongoing Palestinian rocket attacks against Israel, and a close ally of the militantly anti-Israel Hamas radicals who now govern the Palestinian Authority.

Hours after his death, Palestinians in the Gaza Strip fired two rockets into Israel, hitting a building in the southern town of Sderot, but causing no casualties, the military said. No one claimed responsibility.

His appointment as Hamas' top enforcer helped to set the stage for recent Palestinian infighting that has killed 16 people and raised the spectre of all-out civil war between Hamas and the long-ruling Fatah movement it unseated in January's parliamentary elections.

Hamas officials called Abu Samhadana's killing a direct assault on the Palestinian Authority, and vowed to continue its armed resistance against the Jewish state. Abu Samhadana's Popular Resistance Committees faction vowed revenge.

"God willing, our retaliation shall come," blared a loudspeaker on a car carrying Abu Sharif, a top PRC commander, as it toured Gaza streets shortly after the Israeli air strike, which occurred shortly before midnight.

"It will not be by statements, but by rockets toward Sderot and all the Zionist community. It will be by self-sacrificing martyrs who will blow up themselves in every corner."

Hamas lawmaker Mushir al-Masri told Hamas Radio today that "all options are open for the resistance groups to deliver a message to the enemy that must equal the magnitude of Abu Samhadana's loss. "

Since Hamas was elected to power in January, it has not been directly involved in attacks against Israel, but it does back other factions' operations. Hamas is also thought to help finance the PRC, and an estimated 500 people belong simultaneously to both groups.

Over the past week, Hamas members have cooperated with the smaller group in firing rockets at Israel, though Israel has said Hamas leaders did not dispatch them.

Israeli police spokesman Micky Rosenfeld said today that security officials were aware of threats of revenge, and were taking general precautions. He did not elaborate.

No mosque could accommodate the many thousands expected to attend the funeral prayer in the Rafah refugee camp where Abu Samhadana had lived, so a makeshift mosque was set up at the local stadium. Prayer rugs were laid out on the grass, and a stage was built for the preacher to deliver the Friday sermon.

Hundreds of gunmen escorted Abu Samhadana's body from the morgue to his house for a leavetaking ceremony. They fired in the air, chanting, "God is great" and "Revenge, revenge."

The Israeli military said it struck a PRC training camp in the southern Gaza town of Rafah because militants there were planning a large-scale attack on Israel. It would not confirm or deny that Abu Samhadana, the No. 2 man on Israel's wanted list, had been the target.

He was the highest-profile militant commander killed since the Israeli air force targeted Hamas commander Salah Shehadeh in July 2002, dropping a one-ton bomb on his house in Gaza City, killing him and 14 other people, including nine children.

Abu Samhadana, 43, was an explosives expert and a suspect in the fatal 2003 bombing of a US convoy in the Gaza Strip. Israel was infuriated by his appointment as Hamas' security czar.

He and other militants had been about to enter the training camp in the former Jewish settlement of Rafiah Yam when the four missiles struck, killing him and three other militants, and wounding 10.

Palestinian factions, including Fatah, condemned his killing, and said it would not stop attacks on Israel, but fuel them.

Reaction to Abu Samhadana's death swept through the Rafah refugee camp, bringing out nearly all its thousands of residents into the streets immediately after the news broke.

A neighbour, Ibrahim Atwan, 45, recalled that Abu Samhadana had wanted to die a "martyr's" death.

"I feel humbled because men like him gave their lives as a price for their beliefs, and to defend us," Atwan said. His wife, Iman, said she hoped one of her children would "follow in his footsteps."

As a key Israeli target, Abu Samhadana had moved stealthily, switching cars and hideouts. Just a few days before his death, he told The Associated Press in a back alley interview that the US government and its people would " pay a dear price" for leading bruising economic sanctions against the Hamas-run Palestinian Authority for its refusal to disarm militants and recognise Israel.

"We are happy when any American soldier is killed anywhere in the world, because the American Army is an aggressor against all the people in the world, particularly the Arab and Muslim worlds," he said. "The American people are known to be peaceful, so they are asked to move to bring down this terrorist government in Washington, so that the American people are safe from any attacks or retaliation."

He said he had security measures in place against Israeli attack, adding with an ultimately misplaced bravado, "They don't catch me. I hunt them. "

Abu Samhadana graduated from a military school in then-communist East Germany in 1988. He was loyal to Yasser Arafat for many years, but was later expelled from Arafat's group Fatah.

He formed the PRC with militants from various factions, after the latest Palestinian uprising broke out in 2000.