US Secretary of State John Kerry was Saturday seeking to brush aside bitter recriminations and push forward the Israeli-Palestinian peace talks on a third day of shuttle diplomacy.

After five months of mostly sticking to a deal not to air their grievances in public, the mutual distrust between the sides has burst into the open with the top US diplomat's 10th trip back to Israel.

And US officials acknowledged that agreement on a framework to guide the negotiations forward would not be reached on this trip, but would need more time.

Palestinians protested against Kerry as he met Palestinian president Mahmud Abbas in the West Bank for six hours late on Friday.

About 100 people from the left-wing Democratic Front for the Liberation of Palestine (DFLP) waved Palestinian and red flags in Ramallah's central square after Israeli Prime Minister Benjamin Netanyahu accused Abbas and the Palestinians of not being committed to peace.

But Israeli daily Haaretz quoted Kerry as telling American students on Friday that he was still hopeful.

"I am a believer in the possibility... we could achieve something," Haaretz quoted him as telling students in an impromptu appearance at his Jerusalem hotel. "But it will be very, very difficult."

One student was quoted as saying that Kerry explained he was "wading through a volatile cocktail of issues".

Kerry reportedly added that "the US is working with a lot of goodwill, and 'both leaders recognize the consequences of failure'."

The direct negotiations had been frozen for almost three years, but after intense diplomacy by Kerry the two sides agreed to resume talks in July.

Kerry himself came under fire from veteran US Senator John McCain who is also on a visit to Israel.

McCain said he shared Netanyahu's serious concerns about the emerging framework to guide the negotiations into the next phase towards a peace treaty.

"Netanyahu has serious, serious concerns about the plan as has been presented to him, whether it be on the ability of Israel to defend its borders or the reliability of a Palestinian state and their intentions," McCain said in Jerusalem after meeting the premier.

Setting the tone

Top Palestinian official Yasser Abed Rabbo was also unenthusiastic about the proposed framework accord, saying Thursday it "limits Palestinian sovereignty" on the West Bank.

Kerry was to meet Abbas again in Ramallah, and then later Saturday with Netanyahu, with whom he has already held eight hours of talks.

The Israeli leader set the tone when he launched a scathing attack on Abbas at the start of Kerry's visit.

Addressing Kerry, he said: "I know that you're committed to peace, I know that I'm committed to peace. But unfortunately given the actions and words of Palestinian leaders, there's growing doubt in Israel that the Palestinians are committed to peace."

Referring to Israel's release of long-serving Palestinian prisoners as part of the talks, Netanyahu said Abbas had "embraced terrorists as heroes", calling such glorification "an outrage".

US officials have refused to release any details about the framework, but hope to conclude it soon.

It has also not yet been decided whether the document will be made public, but it is unlikely to be signed by both sides.

Kerry stressed the framework was building on ideas from both sides over five months of talks, and would set out the agreements and disagreements on the core issues.

These include the contours of a future Palestinian state, refugees, the fate of Jerusalem, security, "mutual recognition and the end of conflict and of all claims", said Kerry.

The Palestinians want borders based on the 1967 lines of before the Six-Day War, when Israel captured the West Bank, including now annexed Arab east Jerusalem.

But Israel wants to retain existing settlements it has built inside occupied Palestinian territory since then.

Israel also wants to maintain a military presence in the Jordan Valley, where the West Bank borders Jordan.

The Palestinians have insisted there be no Israeli troops in their future state, but are open to the idea of an international force to guarantee security.