(Edits throughout)

By Wafa Amr

RAMALLAH, West Bank, July 18 (Reuters) - Palestinian President Mahmoud Abbas said on Wednesday he will order early parliamentary and presidential elections in response to what he called last month's "coup" by Hamas Islamists in the Gaza Strip.

His fiery speech in the West Bank city of Ramallah underlined the bitterness of the rift between the two territories. Aides said he had no firm timetable for a vote -- it could be in months, or even not for a year or more.

Elections are not due until 2010.

"We will call ... for early legislative and presidential elections and we will not wait for approval from those sitting over there in Gaza or from those sitting abroad," Abbas told a key forum of the Palestine Liberation Organisation (PLO).

Hamas, which won a parliamentary majority in elections last year and routed Abbas's secular, Western-backed Fatah faction in fighting in Gaza a month ago, said it still runs the legitimate Palestinian government and that there could be no new elections if Abbas refuses to negotiate a new national consensus.

Abbas, using uncharacteristically harsh language, said there could be no dialogue with those who staged the "coup" in Gaza unless Hamas first agreed to help organise elections. He first raised the possibility of an early vote last month.

"Hamas dug their grave with their own nails as a result of the crimes they carried out in Gaza," Abbas said. "They have brought upon themselves their loss of legitimacy."

His move came on the eve of a meeting in Lisbon of the Quartet of international powers mediating in the Palestinians' conflict with Israel, their first since the Gaza violence.

The Quartet, which comprises U.S. Secretary of State Condoleezza Rice, the U.N. secretary general and EU and Russian officials, has rallied behind Abbas but it is unclear just how it plans to deal with Hamas and the Palestinian schism.

The group is expected to send its new envoy, former British prime minister Tony Blair, to visit the region this month.

OBSTACLES

With Gaza and the West Bank deeply divided, jeopardising Palestinians' hopes of founding a united state, obstacles to holding elections are substantial.

Analysts said a vote only in the West Bank, where Abbas has enjoyed an end to international sanctions since dismissing the Hamas-led government, might risk further entrenching the split -- and could backfire on Abbas given public disillusionment with Fatah that helped Hamas win last year's election.

Israel and international powers have rallied behind Abbas and cut off the Gaza Strip in rejection of Hamas for its refusal to renounce violence against Israel. A U.N. aid official warned on Wednesday, however, that if the effective trade embargo on Gaza persists, all its 1.5 million people may require food aid.

Senior Hamas official Sami Abu Zuhri told Reuters in Gaza: "The president's call for early elections is unacceptable, unconstitutional and illegal. It will remain only as ink on paper, and neither Abbas nor all the papers (that) support him will be able to hold any election as long as Hamas rejects it."

In Ramallah, pressed to give a timetable for any voting, Nabil Abu Rdainah, an aide to Abbas, told Reuters: "Elections could be held within three months, in a year, or more than year. It depends on the preparations and conditions."

Leading constitutional lawyers have questioned Abbas's appointment of a new government under Prime Minister Salam Fayyad, noting it has not been approved by parliament.

But Abbas defended the legitimacy of his actions. He argues parliament is not functioning -- more than half the legislators in Hamas's majority bloc have been jailed by Israel, and feuding has paralysed the legislature.

Fatah leaders argue the PLO Central Council is a superior body to parliament and can take binding decisions. The Council is expected on Thursday to endorse the call for new elections.

Hamas leaders say that as long as they are not part of the PLO, the Council has no right to act in that way.

Abbas aides have said he is likely to give parliament another chance to convene -- albeit that this is improbable -- before issuing decrees next week to set new elections in train.

Even without a clear timetable for voting, the plan for a ballot will then be part of a framework within which Palestinian leaders may try eventually to resolve their differences.

As part of Israeli and Western efforts to bolster Abbas and Fayyad over Hamas, Israel will free more than 250 mostly Fatah prisoners on Friday and U.S. President George W. Bush has called a major international meeting on the Middle East for the autumn. (Additional reporting by Nidal al-Mughrabi in Gaza and Mohammed Assadi and Alastair Macdonald in Ramallah)

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