Iran’s Supreme Leader Ayatollah Ali Khamenei said he does not expect negotiations with the United States over Tehran’s nuclear program to “reach a conclusion” as Washington toughens its conditions for a deal.

Qatar on Tuesday said it was discussing ideas with Oman to try to bridge the remaining gaps in talks between Washington and Tehran as Iran's supreme leader cast doubts on whether negotiations would reach a conclusion.

DUBAI, United Arab Emirates — Iran and the United States began a fourth round of negotiations Sunday over Tehran’s rapidly advancing nuclear program , officials said, just ahead of a visit by President Donald Trump to the Middle East this week.

The U.S. and Iran remain locked in a standoff over uranium enrichment ahead of a potential new round nuclear talks.