US President Barack Obama’s former Middle East peace envoy Martin Indyk says “distrust” between Israeli and Palestinian leaders is at the heart of their impasse.

“It’s the distrust between the leaders and between the people that holds us up and makes it difficult,” the veteran diplomat told The New York Times in an interview published Thursday, his first since leaving the post last week after peace talks collapsed.

“There’s so much water under the bridge, so much skepticism, so much distrust and lack of confidence,” he said, adding that “the difficulties we faced were far more because of the 20 years of distrust that built up” than because of any core issues that divide the two sides.

Indyk noted that both Prime Minister Benjamin Netanyahu and Palestinian Authority President Mahmoud Abbas agreed on the need to make peace and reach a final agreement that has remained elusive for two decades.

But as time passed, “the sense of urgency wasn’t there on either side,” Indyk told the Times.

“The sense that they have to do it because otherwise they would be overthrown or their governments would fall, didn’t happen,” he said. “It was the opposite.”

Now, Israeli-Palestinian tensions have heated to the boiling point with the discovery Monday of the bodies of three Israeli teenagers who were abducted in the West Bank, and the killing of a Palestinian teenager on Wednesday.

Netanyahu has blamed the Israeli deaths on Hamas, a partner in the new Palestinian unity government, while Palestinians say the other teen’s death was a revenge killing carried out by Israelis.

Indyk, who resigned on Friday, has returned to his post as director of foreign policy at the Brookings Institution, a think-tank in Washington.

But he said he stands ready to work with US Secretary of State John Kerry and the Obama administration in the event of a push for new negotiations.