NABLUS, West Bank: Israeli forces seized a Palestinian cabinet minister and 32 other officials in the occupied West Bank and launched air strikes in the Gaza Strip yesterday, stepping up a campaign against Hamas Islamists.

The move prompted renewed threats from Hamas, which said it would continue to attack Israel with rocket fire.

"Our strikes against the enemy will continue, we have freed the hand of all our cells to strike the enemy everywhere in Palestine," the Hamas armed wing said in a statement.

But Palestinian President Mahmoud Abbas of Fatah demanded Hamas halt firing at Israeli towns immediately so he could negotiate a wider truce with the Jewish state.

Abbas told a news conference in Gaza the rocket shootings were "pointless and needless, they must be stopped". He said that faction heads had agreed to study his proposal.

Hamas official Sami Abu Zuhri said Israel's actions showed any ceasefire call by Abbas was "worthless".

The Islamist group and others said they would consider stopping the rocket firing only if Israel first called off all of its military operations in Gaza and the West Bank. Israel has rebuffed similar demands in the past.

The arrests came after Hamas and other groups turned down Abbas's call for a halt to the rocket firing.

Two months after they formed a unity government, Hamas and Abbas' secular Fatah faction remain at loggerheads. Information Minister Mustafa al-Barghouthi, speaking for the government as a whole, urged international pressure on Israel.

Some 50 Palestinians have been killed in the latest round of factional fighting between Hamas and Fatah. Israeli air strikes over the last eight days have killed at least 35 Palestinians.

In a pre-dawn arrest raid, Israeli troops entered the West Bank city of Nablus and took into custody Education Minister Naser al-Shaer of Hamas, his wife said.

Israeli forces also seized at least three Hamas lawmakers, the mayor and deputy mayor of Nablus and other Hamas officials in neighbouring towns and villages, Hamas officials said.

The Israeli army said in a statement that 33 people had been arrested across the West Bank and were taken for questioning.

Palestinian government spokesman Ghazi Hamad said the arrests displayed "a scale of escalation and Israeli arrogance" and called for those arrested to be released.

"Through this ... aggression the Israeli government is once again pushing the region into a cycle of violence and it bears the full responsibility for the consequences resulting from such irresponsible actions," Hamad said.

The Israeli army said in a statement: "The Hamas terror organization is currently involved in enhancing the terror infrastructure in the (West Bank) region, based on the model used in the Gaza Strip. The organization exploits governmental institutions to encourage and support terrorist activity."

A similar operation last year against Hamas ministers and lawmakers in the West Bank sparked an international backlash.

Israel currently has 44 lawmakers in custody, 40 from Hamas.

Last year's swoop paralyzed the Palestinian parliament, but detained Cabinet ministers were quickly replaced.