Palestinian divisions deepened on Saturday as the Hamas rulers of Gaza rejected president Mahmud Abbas' call for January elections, accusing him of usurping power.

Abbas pledged to pursue reconciliation efforts with the Islamic movement and denied the election call was a "stunt."

But analysts highlighted the challenge he would face in organising elections in Gaza, where Hamas has held sway since mid 2007.

"We are going to pursue our efforts for reconciliation" with Hamas, Abbas said a day after calling presidential and legislative elections for January 24.

Abbas issued a decree late Friday calling elections in Jerusalem, the West Bank and Gaza, in a move seen as turning up the heat on the Islamist group to sign a much-delayed Egyptian-brokered deal for Palestinian unity.

Hamas -- which trounced Abbas's secular Fatah faction in the last parliamentary elections in January 2006 -- rejected the move.

"This is an illegal and unconstitutional step because Abu Mazen's (Abbas's) tenure is over and he has no right to issue any decree concerning this" election, Hamas spokesman Fawzi Barhum told AFP on Friday.

Abbas was elected on January 9, 2005 for a four-year term. The Palestinian Authority extended his presidency by one year so presidential and parliamentary elections could be held on the same date.

Hamas has consistently rejected the extension granted to Abbas, and does not consider him to be the legitimate president of the Palestinian people.

Barhum said Abbas was making a "deliberate attempt to make (Palestinian) divisions permanent," by calling elections for January.

And on Saturday, Hamas said Abbas -- whose term in office expired in early January 2009 -- should be put on trial.

Abbas "must be tried for usurping power," deputy Palestinian parliamentary speaker Ahmed Bahar told a news conference in Gaza City.

The decree calling elections "has no value whatsoever from a constitutional point of view," he said.

Hani al-Masri, a Ramallah-based political analyst, said the calling of elections is a "political tactic" aimed at twisting the arms of Hamas leaders to sign the reconciliation deal.

"But there is a (big) step between the publication of a decree and the holding of elections on the ground," he said.

Mukhaimar Abu Saada, lecturer in political sciences at Gaza's Al-Azhar University, predicts a heightened war of words between Hamas and Abbas's Fatah.

The split between the factions has become "the central question" for Palestinians, even more important than the question of Israeli settlements in the West Bank.

Tension could mount still further if Hamas decides to call elections in the Gaza Strip, the academic said.

"That would lead to political division and a permanent break" between Hamas and Fatah," Abu Saada said.

On Saturday Abbas said he was determined to proceed with organising the polls.

"The elections decree is very serious; it is not a stunt," he told delegates of the Palestine Liberation Organisation's Central Committee gathered in Ramallah.

He insisted, however, that he would not close the door on efforts brokered by Egypt to patch up deep divisions between Hamas and Fatah.

"Even if we don't succeed now, we will try again because reconciliation is in the interest of the Palestinian people," Abbas said.

Egypt this month proposed an agreement that would see new elections being held in June next year. Fatah has signed the accord but Hamas said it needs more time to study it.

Simmering divisions boiled over in June 2007 when Hamas fighters expelled Abbas loyalists from Gaza in a week of bloody clashes, seizing control of the impoverished and densely populated territory.