US Secretary of State John Kerry and Palestinian president Mahmud Abbas held "constructive" talks on the Middle East peace process, a US official said Thursday, as crunch decisions loom in the coming days.

After earlier talks with King Abdullah II in Amman, Kerry and his team met for more than four hours over dinner in the Jordanian capital with the Palestinian leader, a senior State Department official said.

Describing it as "a constructive conversation," the official added that "the secretary plans to remain engaged with both President Abbas and Prime Minister (Benjamin) Netanyahu over the coming days".

Israel is due to release a fourth and final tranche of prisoners over the weekend, a move which will prove key in deciding whether the talks, resumed in July after a three-year gap, unravel or not.

Under the deal relaunching the peace negotiations, Israel said it would release 104 Arabs held since before the 1993 Oslo peace accords in exchange for the Palestinians not pressing their statehood claims via the UN.

Israel has so far freed 78 prisoners but there are growing Netanyahu's cabinet may block the final releases, particularly of Israeli Arab militants.

In Jerusalem, about 50 relatives of the victims of attacks demonstrated Wednesday near Netanyahu's residence against widening the prisoner releases.

"Justice and values come before politics. We can't reach peace by ignoring the blood of the victims," said Meir Indor, a spokesperson for the families.

Palestinian minister of prisoners affairs Issa Qaraqe told Voice of Palestine radio that "Israel is trying to worm its way out of releasing the prisoners. They will be held responsible for any repercussions of this."

He insisted Israel free all the prisoners.

- League rejects 'Jewish state' -

The Palestinians also won key backing Wednesday from the Arab League for their refusal to bow to Netanyahu's demand to recognise Israel as "the nation state of the Jewish people."

"We express our total rejection of the call to consider Israel as a Jewish state," an Arab League declaration said at the end of a two-day summit in Kuwait.

But the Israeli side hit back that Abbas's stand on the issue "could torpedo the peace process."

The Palestinian leader had "boasted that he refuses to even discuss recognising the Jewish state, once again parading rejectionism as virtue," a senior Israeli official said.

Kerry, who coaxed the two sides back to the negotiations last July after a three-year freeze, is aiming to reach a framework to guide the talks going forward as an April 29 deadline for a deal looms.

But Abbas told him he would not discuss the framework accord until after the prisoner releases have taken place, a Palestinian source said.

Israel also wants the Palestinians to agree to extend the talks beyond April 29, warning a failure to do so would scupper the final prisoner release.

"We don't need a new series of accords so that Israel can bury them under an avalanche of conditions, reservations or interpretations before going back on their commitments," Abbas told the Arab League.

The prisoner issue is not the only issue jeopardising the peace talks.

Israeli army radio said Wednesday the US had offered to release Jonathan Pollard, who was arrested in 1985 and condemned to life imprisonment for spying on the United States for Israel, in return for Palestinian prisoners being freed.

But State Department spokeswoman Jen Psaki shot down the report, saying: "There are currently no plans to release Jonathan Pollard."

Kerry was flying back to Rome early Thursday to join up again with Obama for a meeting with Pope Francis.

The two Americans will then visit Saudi Arabia on Friday, when the peace process is likely to be one of the issues topping the agenda in talks with Saudi King Abdullah.