AFP - Israel launched a new crackdown on Hamas on Thursday, rounding up top leaders in the West Bank after the failure of efforts to secure the release of a soldier held by the Islamist rulers of the Gaza Strip.

Security forces seized 12 senior Hamas leaders in pre-dawn raids in the occupied West Bank, including four members of the Palestinian legislative council, Hamas and the army said.

The Islamists denounced the action as "blackmail" following the collapse of Egyptian-brokered efforts to reach an agreement on an Israel-Hamas prisoner swap.

The Palestinian Authority, headed by Hamas's political foes Fatah, also slammed the arrests and called on the international community to intervene.

"These men have been the leaders of the ongoing effort to restore the administrative branch of the Hamas terror organisation in the region, while attempting to strengthen the power and influence of Hamas," an Israeli military spokeswoman said.

Thirty-six Hamas MPs have been in jail since a major crackdown in the West Bank that followed the capture of Israeli soldier Gilad Shalit by Gaza militants including Hamas fighters in a deadly cross-border raid in June 2006.

On Saturday, Shalit will have been held captive for 1,000 days.

Among those arrested were Nasseredin al-Shaer, who was deputy premier in the short-lived Hamas government formed in March 2006, and two senior Hamas officials in the West Bank, Raafat Nassif and Adnan Asfur, the group said.

Western-backed Palestinian prime minister Salam Fayyad condemned the arrests and called on the international community to intervene "to pressure Israel to immediately free all members of Palestinian parliament whom they are holding."

A spokesman for president Mahmud Abbas, whose forces were booted out of Gaza by Hamas in June 2007 after deadly factional fighting, blasted the arrests as "kidnappings" aimed at torpedoing reconciliation talks under way between Fatah and Hamas in Cairo.

The arrests follow the failure this week of the Egyptian-mediated negotiations for a prisoner swap that would entail the release of Shalit in exchange for hundreds of Palestinians held in Israel.

The collapse of the talks led Israel to examine ways of getting tougher with the Islamists, including imposing harsher conditions for Hamas detainees.

Among the steps being considered are limiting cash transfers to prisoners, restricting their access to television and radio, reducing visiting rights and opportunities for education as well as limiting contact between the prisoners.

Israel is also considering tightening the crippling blockade it has imposed on the Gaza Strip since Hamas seized power in June 2007.

Senior Hamas leader Salah al-Bardawil claimed the West Bank arrests aimed at pressuring the Islamist group to cave in to Israel's demands in the prisoner swap negotiations.

"It is a flagrant attempt to put pressure on Hamas and force it to make concessions and accept an exchange of prisoners without Israel having to pay the price," Bardawil said in a statement published on the Hamas website.

"This blackmail attempt is destined to failure."

More than 11,000 Palestinian prisoners are held in Israeli jails, including thousands of members of Hamas, which Israel -- like the European Union and the United States -- considers a terrorist organisation.

Hamas won 74 of the Palestinian legislative assembly's 132 seats in the January 2006 election when it trounced Abbas's secular Fatah faction but its government was boycotted by the West and attempts to form unity governments failed.

The human rights group Public Committee Against Torture in Israel called on the justice minister to shun steps that would worsen prison conditions, branding any such move "unlawful collective punishment."