WASHINGTON (Reuters) – President Barack Obama voiced frustration on Tuesday over stalled Middle East peace efforts, saying Israelis and Palestinians may not be ready to resolve their conflict no matter how much pressure Washington exerts.

Obama, speaking to reporters after hosting a nuclear security summit, made clear he harbored little hope for swift progress toward Middle East peace, more than a year after taking office and declaring it a high priority for his administration.

U.S.-led peace moves have been stymied by a dispute over Jewish settlement construction on occupied land that has strained ties between Washington and its close ally Israel, and by divisions among the Palestinians.

“The truth is in some of these conflicts the United States can’t impose solutions unless the participants in these conflicts are willing to break out of old patterns of antagonism,” Obama told a news conference.

The Obama administration has tried to get Israel and the Palestinians to launch indirect peace talks but has made scant headway. Israeli Prime Minister Benjamin Netanyahu gave little ground in White House talks with Obama last month.

Obama recently acknowledged he had underestimated the obstacles to a renewed peace process that bedeviled many of his predecessors, and some critics have called his approach naive.

“The Israeli people, through their government, and the Palestinian people, through the Palestinian Authority, as well as other Arab states may say to themselves, ‘We are not prepared to resolve these issues no matter how much pressure the United States brings to bear,'” Obama said.

But Obama insisted the United States would press on, “constantly present, constantly engaged.”

He said progress on issues like Middle East peace, nuclear nonproliferation and nuclear disarmament would be measured “not in days, not in weeks.”

“It’s going to take time, and progress will be halting,” he said. “And there will be frustrations.”

The White House promised on Friday not to “surprise anybody at any time” with a dramatic shift in Middle East peace strategy and said no decision had been made for Obama to offer his own solution to the conflict.

While dampening expectations for a revamped U.S. approach, national security adviser Jim Jones left open the possibility of further internal discussions, following reports a broad new Israeli-Palestinian peace proposal was under consideration.