Fatah accused Hamas supremo Khaled Meshaal of being hysterical for saying on Friday, in a thinly veiled reference to Abbas, that he was part of a plot to undermine Hamas and remove it from power.

"We view Khaled Meshaal's speech with concern," a statement said, referring to an address to an enthusiastic crowd of supporters in a Palestinian refugee camp in a Damascus suburb.

"We can only describe this speech as divisive, because it aims to provoke tensions in the Palestinian territories and spark civil war."

The war of words began when Abbas vetoed a Hamas government decision to create a new special force of armed militants headed by a wanted radical.

The move, the first time Abbas has revoked decisions of the new Hamas-led government, followed US criticism of the security appointment and Israeli threats to target the militant in question.

In response, Meshaal told his audience: "What is happening in Palestine is a policy carried out by a parallel government, a counter-government which deprives us of our prerogatives and the people of their rights. It is a plot.

"A certain part of our people is plotting against us. They are carrying out a premeditated plan which is aimed at our undoing."

In its harsh response, Fatah said the speech was by "a man whose ambition is and always has been to cause Palestinian blood to flow ... while he lives in (Damascus exile) and benefits from the experiences of certain people to provoke divisions and civil wars."

It described Meshaal's remarks as "hysterical," and the speech as "full of plots, calumnies, lies and deception."

A member of the Al-Aqsa Martyrs' Brigades, an armed offshot of Fatah that would theoretically participate in the Hamas-proposed security body, rejected Meshaal's comments and called for an apology.

"Khaled Meshaal should apologise and (prime minister) Ismail Haniya should explain himself, because he is a member of the Hamas politburo," he said at a press conference in Gaza City, without giving his name. "We reject these kinds of statements."

Only hours before the news of Abbas's decree, Haniya declared his backing for the new force.

Since Friday night, pro-Abbas groups have been demonstrating in both the Gaza Strip and the West Bank.

Around 500 Al-Aqsa members marched in the West Bank city of Ramallah, shouting: "Long live President Abbas" and "Khaled Meshaal wants to start a civil war".

In Nablus, demonstrators shouted: "Meshaal has sold out to Syria and Iran," while others temporarily occupied the courthouse and demanded an apology.

Abbas and Hamas have been sharing power uneasily since Meshaal's group won an upset victory in January general elections, unseating Fatah and ending its grip on power of more than a decade.

The moderate Palestinian Authority president is committed to negotiating a peace deal with Israel. Hamas continues to refuse even to recognise the Jewish state, much less renounce violence against it and honour previous Palestinian agreements.

On Thursday, Siam said he was creating a new special security force of gunmen from armed factions to supplement the work of Palestinian police and security forces in clamping down on rampant chaos in the territories.

He nominated top Gaza-based militant Jamal Abu Samhadana, who is wanted in Israel for scores of attacks, to a senior position in the interior ministry to oversee various security elements, including the new force.

A Palestinian official said Abbas had drawn up a decree to reverse the decisions and that it had been approved by the executive committee of the Palestine Liberation Organisation on Friday.

Hamas spokesman Ghazi Hamad said Mohammed Awad, general secretary of the government, would meet with Abbas presidential secretary Rafiq Husseini on Saturday to try to defuse the controversy.

And Deputy Prime Minister Nassereddine al-Shaer issued a conciliatory statement, saying Meshaal's remarks "do not represent the view of the Palestinian government."

He called on all Palestinians to "preserve national unity and to protect the higher interests of the Palestinian people."

In an interview with AFP, Abbas flatly denied any power struggle with Hamas, instead referring to "confusion" given the administration's inexperience.

He begins a European tour Sunday aiming to convince foreign donors to continue aiding the Palestinians despite the Western boycott of Hamas and the suspension of direct EU and US aid to its government.