A senior Palestinian official on Wednesday added his voice to calls for the replacement of international Middle East envoy Tony Blair, but the office of Palestinian President Mahmoud Abbas said it would carry on cooperating with the former British leader.

"The Palestinian presidency will continue to work with the envoy of the international Quartet Committee Tony Blair in his capacity as the choice of the Quartet," presidential spokesman Nabil Abu Rdainah said in a brief statement.

It made no direct reference to calls from senior Palestinians for the replacement of Blair, whom they accused of bias in favour of Israel.

Mohammed Ishtayeh, a member of the Central Committee of the dominant Fatah movement and a confidant of Abbas, told Voice of Palestine radio earlier on Wednesday that Blair was no longer trusted to be an impartial mediator.

Ishtayeh said the Palestinians had also written to the Quartet of mediating powers which Blair represents -- the European Union, United States, Russia and United Nations -- to say its latest proposition for a resumption of stalled peace negotiations was too vague to be meaningful.

Quartet envoys were due to meet in Brussels on Sunday.

"We do not expect much of the Quartet. There is discontent with its envoy Mr. Tony Blair," Ishtayeh said. "Our general evaluation of his efforts is that he has become of no use at all. He has developed a large bias in favour of the Israeli side and he has lost a lot of his credibility.

"We hope the Quartet will reconsider the appointment of this person," he added, in the most explicit public suggestion to date that influential Palestinians want Blair to go.

The presidential spokesman did not allude to recent negative statements about the envoy.

FOCUS ON QUARTET

Abu Rdainah urged the Quartet, and Blair, to "exert every possible effort to compel Israel to accept the last statement of the Quartet committee by deeds, not words, through finding a mechanism to stop (Jewish) settlement in Palestinian lands".

A call by the Quartet for the rapid resumption of talks without preconditions was turned down by the Palestine Liberation Organisation last week but accepted by Israel.

The Palestinians say the Quartet failed to explicitly require Israel to stop building on occupied land in the West Bank and East Jerusalem -- the only condition under which they will agree to restart direct peace talks.

The Quartet formula demanding that neither side undertake unilateral acts which could interfere with the talks was simply too vague, PLO official Ishtayeh said.

"I believe the Quartet needs to work on itself more than anything else ... The situation does not permit ambiguity. Either settlement stops or there will be no negotiation."

A spokesman for Blair said Ishtayeh's comments did not reflect Blair's conversations with the Palestinian leadership.

He said it was the role of the Quartet representative to interact with both sides "not least so that we can continue to deliver change on the ground for Palestinians to improve their quality of life".

Blair has been the Quartet's envoy since 2007, focusing on easing the practical conditions of Israel's military occupation of the West Bank so the Palestinian economy can develop and form a solid foundation on which Abbas's Palestinian Authority can build the infrastructure of a future state.

The economy has grown and in the past two years Palestinian Prime Minister Salam Fayyad has created most of the attributes of statehood, in government institutions, administration and security. But Israeli forces remain in ultimate control.

Since peace talks collapsed a year ago, with the expiry of an Israeli moratorium on settlement construction, the Palestinians have shifted the focus of their efforts to a bid for statehood at the United Nations, where Abbas formally lodged an application for full membership last month.

The United States has said it will veto that step, insisting along with Israel that a Palestinian state can only come into being via a negotiated, comprehensive treaty with Israel to resolve the 63-year-old Middle East conflict.