US Secretary of State John Kerry on Monday issued a stark warning to Israel to resume long-stalled peace talks with the Palestinians, saying if efforts fail now they may never get another chance.

"We are running out of time. We're running out of possibilities... If we do not succeed now, we may not get another chance," Kerry told a forum in Washington organized by the American Jewish Community lobbying group.

His warning came amid reports that he is planning to return to the Middle East region within days for his fifth trip to Israel since he launched his bid to kickstart the negotiations in early February.

"We can't let the disappointments of the past hold the future prisoner. We can't let the absence of peace become a self-fulfilling prophecy," Kerry urged in one of his most passionate speeches to date on the elusive search for peace.

Urging the Jewish forum to reflect on what will happen if his peace efforts fail, Kerry said "the absence of peace becomes perpetual conflict."

"We will find ourselves in a negative spiral of responses and counter-responses, that can literally slam the door on a two-state solution, having already agreed, I think, that there isn't a one-state one," Kerry said.

"And the insidious campaign to de-legitimize Israel will only gain steam," he said.

When Palestinian president Mahmud Abbas sought upgraded UN observer status at the UN General Assembly last year, only nine countries voted against. Kerry warned next time even fewer nations might oppose such a move.

Over the past four months, the top US diplomat has been engaged in intensive shuttle diplomacy aimed at finding a way back to some form of direct talks which have been in deep-freeze since late 2010.

He last visited Jerusalem and Ramallah on May 23-24 for what was his fourth visit in just over two months -- the same number of trips to Israel and the Palestinian territories as his predecessor Hillary Clinton made during her four-year tenure.

Kerry has insisted he is pursuing a quiet strategy, and will not reveal the contours of his plan until the two sides have made the tough decisions needed to return to the talks.

While the United States "will always have Israel's back," it would be even better "if we had some more company," Kerry said.

"With the right choices and enough courage and determination there's a very different future possible for Israel."

And he vowed that "peace pays" for both the Israelis and the Palestinians.

"I assure you that a stable Palestinian state with assured borders and a flourishing economy will only strengthen Israel's security and Israel's future," he said.

"Resolving this conflict for both sides can have far-reaching benefits that will be in everybody's interests. And the reverse is also true. Not resolving this will result in serious consequences for both."

While he acknowledged that there was deep-rooted skepticism and even cynicism, he said everyone must seize the opportunity ahead.

"In this conflict, the simple fact is tomorrow is not guaranteed to look like today. And the people who think somehow that because there's a fence and because there's been greater security and fewer people hurt are lulling themselves into a delusion that that somehow can be sustained. It cannot be," he said.

He also warned Israelis of the consequences of allowing the Palestinian Authority to collapse, raising the specter of another intifada.

"The failure of the modern Palestinian leadership could very well invite the rise of the very thing that we want to avoid. The same extremism in the West Bank that we have seen in Gaza or from southern Lebanon."