Iran said Sunday it no longer will comply with limits on uranium enrichment under its 2015 nuclear pact, as hundreds of thousands gathered across the country to mourn the death of a military leader killed Friday in a U.S. airstrike in Iraq.

Sunday’s move and Maj. Gen. Qassem Soleimani’s death opened a new chapter in Iran’s tense relationship with Western nations, pushing the nuclear accord closer to collapse and raising the risk of a military confrontation with the U.S.

In its announcement on Iranian television Sunday, Tehran stopped short of an abrogation of the nuclear pact, which limited the country’s nuclear program in return for lifting multination sanctions.

But its decision, the latest step by Iran to scale back compliance with the deal, means Tehran could install new centrifuges—machines that produce enriched uranium—and further ramp up the purity of the fuel it produces closer to weapons-grade material.

That would allow Iran to reduce to less than six months the time needed to amass enough nuclear fuel for one bomb, once it reinstalls a sufficient number of its centrifuges, a process expected to take months, nuclear experts have said.