London – Well-informed western sources said that the United States and its Western allies were exerting pressure on Iran to take steps to sharply cut the amount of radioactive material it holds in an attempt to bolster last year’s nuclear deal and discourage the incoming Donald Trump administration from abandoning it.

The Wall Street Journal reported on Saturday that discussions about reducing Iran’s stockpile of enriched uranium started months ago and were among a number of measures President Barack Obama’s administration has been examining to fortify the accord in its final months in office.

The election of President-elect Donald Trump created fresh uncertainty around the deal.

On Wednesday, Iran’s Supreme Leader Ayatollah Ali Khamenei threatened a response if the U.S. extended Iranian sanctions—as House lawmakers this week voted to do—for another decade.

Sources quoted by the WSJ said plan that the U.S. and its partners were currently discussing with Iran would take Tehran’s stockpile far from the 300-kilogram limit on enriched uranium, ensuring that it wouldn’t exceed the cap for some time.

Last week, the head of the United Nations atomic agency overseeing the Iranian nuclear agreement called out Iran for exceeding the heavy-water cap for a second time this year. International Atomic Energy Agency Director General Yukiya Amano warned that Iran could undermine confidence in the implementation of the deal if Tehran crossed key limits again.

Iran reacted swiftly and sent 11 tons of heavy water to Oman early this week, likely putting Iran below the 130-metric-ton limit for months to come, people familiar with the situation said.

Western officials told the WSJ that Iranian officials have engaged in serious discussions about the new plan but haven’t so far committed to it.