US Middle East envoy George Mitchell has held talks with Palestinian leader Mahmoud Abbas in the West Bank, as part of renewed US peace efforts.

Mr Abbas's top negotiator said the meeting had been "positive" and called on both sides to stick to commitments made under the 2003 "roadmap".

On Monday Mr Mitchell met Israeli Prime Minister Benjamin Netanyahu.

He reiterated calls for a two-state solution, which the Israeli leader has refused to endorse.

Mr Netanyahu is scheduled to give a major foreign-policy speech on Sunday.

Under the staged "roadmap" peace plan, Israel agreed to freeze settlement activity and remove unofficial settlements known as outposts.

The Palestinians agreed to dismantle militant organisations and carry out reforms.

Israeli outposters vow to stay

"The Obama Administration has made clear... its expectation that both parties implement their obligations," Palestinian negotiator Saeb Erekat said.

He said the emphasis was a "litmus test of fairness and balance in America's approach to Middle East peace".

While the Palestinians had made "significant progress" on their obligations, "Israel has failed to implement any" of its commitments, he said.

Mr Mitchell is visiting in the wake of US President Barack Obama's keynote speech in Cairo last week.

Mr Obama called for a "new beginning" between Muslims and the US and described the Palestinians' situation under in exile in neighbouring countries and under Israeli occupation as "intolerable".

Ambitious goal

Earlier this week Mr Mitchell said the US was striving for "a Palestinian state, side by side in peace and security with the Jewish state of Israel".

Amid speculation that the prime minister may back a two-state solution on Sunday, centre-left Israeli Defence Minister Ehud Barak warned that failure to reach such an agreement would result either in a state that was no longer Jewish, or an "apartheid regime".

Benjamin Netanyahu is understood to back Palestinian self-rule in an entity which has no army and does not control its own airspace or borders.

President Obama seems to hope he can achieve a historic Middle East settlement within his first term and this ambitious goal puts him on a collision course with Mr Netanyahu's government, the BBC's Paul Wood in Jerusalem says.

The immediate clash, however, will come over the issue of Jewish settlements built on land occupied by Israel in the 1967 war, our correspondent says.

Mr Obama has said more clearly than any US president for a long time that settlement building must stop, while Mr Netanyahu is sticking to the established Israeli formula that there should be "natural growth" in existing settlements.

After his talks with Mr Netanyahu, Mr Mitchell stressed the "unshakeable" US commitment to Israeli security, amid Israeli fears over increased US pressure.

"We come here to talk not as adversaries in disagreement but as friends in discussion," he said.

After Israel and the West Bank, the US envoy is to head to Lebanon before visiting Syria on Friday and Saturday as part of increased diplomatic engagement by the Obama government with Damascus.

The Palestinian Authority says it will not return to negotiations with Israel unless it freezes Jewish settlement activity in the West Bank and openly backs a two-state solution to the Israeli-Palestinian conflict.