U.S. Middle East envoy George Mitchell met Israeli Prime Minister Benjamin Netanyahu on Thursday for the second time in two days before the expected start of indirect Israeli-Palestinian peace talks.

The United States hopes the two sides will embark on negotiations in an indirect format in the coming days, a U.S. spokesman said on Wednesday, after the first, three-hour meeting between Netanyahu and Mitchell.

Neither side commented on the details of Thursday's meeting.

An Israeli political source, speaking on condition of anonymity, said the start of indirect "proximity" talks had not been announced as expected on Wednesday because Palestinian President Mahmoud Abbas had yet to formally agree to join them.

Mitchell will meet Abbas on Friday and Saturday, U.S. officials said.

The Arab League approved Abbas' participation in the talks last Saturday, and he is awaiting formal approval from the Palestine Liberation Organisation's Executive Committee this Saturday, said his spokesman, Nabil Abu Rdainah.

"If the executive approves these indirect negotiations, all the final-status issues will be on the table for discussion," Rdainah said. "Absolutely no issue will be excluded and Jerusalem will be the top priority."

Israeli leaders have said the Palestinians can raise core issues in the indirect talks but only direct negotiations can resolve them. The indirect format for talks would involve Mitchell shuttling between the two negotiating teams.

Washington opted for this method after failing to narrow differences over Israeli settlement activity enough to resume face-to-face talks, which the sides have not held in 18 months.

The period without peace talks has included Israel's Gaza offensive, election of a right-wing Israeli government and entrenched rule in the Gaza Strip by Hamas Islamists opposed to the U.S. peace efforts.