US Secretary of State John Kerry insisted Thursday that Israel's security is a top priority for Washington, both in nuclear talks with Iran and peace talks with the Palestinians.

Kerry held a day of talks with Israeli and Palestinian leaders aimed at driving forward peace negotiations which appear to have made little headway since beginning under his patronage in late July.

A senior Palestinian official described the negotiations as being at "a very difficult" stage.

But Iran was also a central issue when Kerry met Israeli Prime Minister Benjamin Netanyahu for more than three hours in their first face-to-face meeting since their political falling out over the Iran nuclear deal.

"I can't emphasise enough that Israel's security in this negotiation (with Iran) is at the top of our agenda," Kerry said at a joint news conference in Jerusalem.

"The United States will do everything in our power to make certain that Iran's nuclear programme of weaponisation possibilities is terminated."

Kerry stressed the two men had also spent "a very significant amount of time" discussing the peace talks with the Palestinians.

"Israel's security is fundamental to those negotiations," he said.

The US top diplomat reiterated the importance of security after a three-hour meeting with Palestinian president Mahmud Abbas in the West Bank city of Ramallah.

"We are not going to discuss this further publicly," Kerry told reporters afterwards, saying only that their discussions on security had made "progress".

"The interests are very similar, but there are questions of sovereignty, questions of respect and dignity, which are obviously significant to the Palestinians, and for the Israelis very serious questions of security.

"Shortly, perhaps in a week or so, I may return for further discussions, depending on where we are," Kerry added.

Abbas himself made no appearance after the meeting.

'Situation still very difficult'

"Abbas met Kerry for four hours... and discussed issues including security," Palestinian negotiator Saeb Erakat told AFP.

"We hope Israel will stick to its commitments and be forced to stop settlement building. Settlements are the reason for the difficulties in negotiations," Erakat said.

"The situation is still very difficult and matters are complicated."

A Palestinian official speaking on condition of anonymity said Kerry's security proposals "were very bad ideas which we cannot accept".

After meeting Abbas, Kerry returned to Jerusalem for dinner with Netanyahu, and a senior State Department official said the two would meet again on Friday morning.

Kerry would also meet Israeli Finance Minister Yair Lapid before leaving for Washington, the official said.

US special envoy on security General John Allen briefed Netanyahu Thursday, Kerry said, on "potential threats to Israel (and) to the region".

US and Israeli media reports have suggested Allen was to present an outline of how Israel's security arrangements might look under a peace deal, but a State Department official denied Allen had a ready-made plan.

Kerry and Allen, who has been working on the security issue with Israeli defence experts, provided Netanyahu and his top brass "with some thoughts about... security challenges that we're going to be facing, that the Israelis are facing," deputy State Department spokeswoman Marie Harf said in Washington.

"This isn't a plan, per se. This is really part of an ongoing conversation," she told reporters. "More details certainly were provided, but it would be incorrect to say that some final plan was put on the table for discussion."

Netanyahu said that under any peace agreement, Israel "must be able to defend itself, by itself, with our own forces" -- an allusion to the reported debate over security in the Jordan Valley, which separates the West Bank from neighbouring Jordan.

Israel has always insisted that in any final agreement, it would have to maintain a military presence there, and has rejected outright the idea of any third party involvement.

Maariv newspaper said that Allen was to have outlined a "bridging proposal" which would enable Israel to reduce, as much as possible, its military presence in the Jordan Valley.

But Deputy Defence Minister Danny Danon insisted Israel would not compromise on security there and "not outsource its basic security needs to the Palestinians".

Alarmist Israeli rhetoric on Iran, which commentators say also deliberately sidelines the Palestinian issue, was heavily criticised by a former head of the Shin Bet internal security service on Wednesday.

"The consequences of not having a solution to the Israeli-Palestinian conflict are more existential than the Iranian nuclear project," Yuval Diskin told a conference in Tel Aviv.

"Israel must freeze settlement building immediately" in order to reach a much-needed agreement with the Palestinians, Diskin said.