US Secretary of State John Kerry insisted Sunday concrete progress has been made in peace talks between Israelis and Palestinians, but said details will be kept under wraps.

Kerry, who has made nine trips to the Middle East since March and helped launch nine-month direct talks between the two sides in July, said talking about any agreements could be counterproductive.

"I'm personally encouraged that very tough issues are beginning to take shape," he said in an interview with ABC's "This Week."

"But we've agreed not to be talking about what we're doing because it just creates great expectations. It creates pressure. It creates opposition, in some cases.

"I think it's much better for us to do exactly what we've been doing, which is negotiate quietly and privately," he continued.

Israeli and Arab media reports say the plan envisaged by Washington would see Israel maintain a military presence on the border after a peace agreement with the Palestinians.

An international force would be acceptable to the Palestinians, but Israel opposes such a solution.

Israel has always insisted that a continued military presence on the frontier would be vital for its security for some 10-15 years after Palestinian statehood.

Before Kerry's latest trip to the region, he had said "we are closer than we have been in years" to reaching a deal. And State Department spokeswoman Jen Psaki had said the United States was "focused on a final deal" rather than an interim agreement.

On Sunday, Kerry expressed optimism that this was "a different moment" for the conflict that could allow "a different set of choices" than in past, failed efforts.

"I think that the dynamics of the Middle East offer a different moment, the possibilities of peace with the Arab League, the realities of what might and might not stare people in the face if you don't get an agreement," he said.

"And hopefully, the leaders will seize this moment and at least move the ball forward somewhat."

But he cautioned that the conflict has "confounded presidents and secretaries state for 30 or 40 years."

"If this conflict was easy ... this would have been done years ago," he said.