Palestinian President Mahmoud Abbas said in televised speech Thursday that a release of all Palestinian prisoners must be part of any peace deal with Israel.

Abbas delivered the televised address Thursday to mark Palestinian Prisoners' Day. About 8,500 Palestinian prisoners are held in Israeli jails and detention centers. Israeli and Palestinian negotiators are trying to reach a peace deal by the end of the year.

Rallies and marches are planned throughout the West Bank on Thursday to mark Prisoners' Day. The fate of prisoners is one of the most emotionally charged issues of the Israeli-Palestinian conflict. Palestinians see prisoners as heroes in the struggle for statehood. To many Israelis, they are terrorists out to destroy the state.

On Thursday, Abbas said that a Middle East peace conference will be held in Moscow in June.

"We have great hopes the conference will move forward the peace process between Palestinians and Israel, and that it will lay the grounds for the overall peace process for the entire Middle East that will include Syria and Lebanon," Abbas said in a lecture at a Moscow university.

Abbas is expected to meet with Russian President Vladimir Putin at the end of his three-day visit Friday.

Israel has been cool to the idea of a Moscow conference, which Russia proposed immediately after the Annapolis talks in November. The conference would likely put a greater emphasis on bringing Israel and Syria back to the negotiating table after eight silent years.

Putin is due to return to Moscow on Friday after visiting Libya and Italy.

Russia is a member of the so-called Quartet seeking to broker Middle East
peace, along with the United States, the European Union and the United
Nations.

Unlike other Quartet members, Russia recognizes the legitimacy of Hamas, the militant party that holds a majority of seats in the Palestinian parliament. That could give Russia considerable influence as a mediator, observers say.

Hamas is unlikely, however, to be invited to the conference.

Abbas' visit to Russia is his fourth as Palestinian leader. He earned a
doctorate in history at Moscow State University in the 1980s.