Japan on Monday urged Iran to follow its commitments under a 2015 nuclear agreement with major powers and refrain from taking further actions to undermine it, after Tehran said it had started enriching uranium above the limit set by the deal.

“We are deeply concerned about Iran’s announcement” on Sunday, Deputy Chief Cabinet Secretary Yasutoshi Nishimura said at a news conference. “We strongly urge Iran to abide by the nuclear agreement, immediately return to its commitments and refrain from taking steps that would damage the accord.”

Japan, which has built amicable ties with Iran, has supported the nuclear deal as a way to promote stability in the Middle East.

“Japan will continue to play its role in easing tensions and stabilizing the situation in the Middle East in collaboration with other countries. We believe the issue should be resolved through dialogue,” Nishimura said.

Iran’s atomic energy agency said the country has started increasing uranium enrichment to above the 3.67 percent cap agreed under the 2015 deal with Britain, China, France, Germany, Russia and the United States.

Middle East tensions have heightened in recent months amid a U.S.-Iran standoff over the nuclear accord, from which Washington withdrew in 2018.

Tehran’s latest move, which came about a week after it said it had exceeded the accord’s limit on the amount of low-enrichment uranium it can stockpile, is meant to pressure the other signatories into delivering economic relief from crippling U.S. economic sanctions.

Following Iran’s announcement Sunday, U.S. President Donald Trump warned that Tehran should “be careful,” while Secretary of State Mike Pompeo said in a tweet that the Middle Eastern country’s action would “lead to further isolation and sanctions.”

A year after the U.S. withdrawal that led to the reinstatement of economic sanctions, Iran said in May it was suspending some of its commitments under the nuclear deal.

The other five countries involved in the deal have struggled to respond since Iran set a 60-day deadline until early July to negotiate new terms for the accord. Under the original agreement, sanctions on Iran were lifted in exchange for curbs to its nuclear program.