United Nations Secretary-General Antonio Guterres told an emergency meeting of the U.N. Security Council called by Iran that “We cannot – and must not – give up on peace.”

Guterres called the U.S. strikes on Iran’s nuclear facilities “a perilous turn in a region already reeling,” adding that “Peace cannot be imposed, it must be chosen.”

He urged immediate and decisive action to halt the fighting and return to “serious, sustained negotiations” on Iran’s nuclear programme to find a verifiable solution with full access by U.N. nuclear inspectors and a restoration of trust.

In urging a return to diplomacy and a peaceful solution, Guterres stressed Sunday that one path leads to wider war and the other to de-escalation and dialogue. “We know which path is right,” he said.

The U.S. military struck three sites in Iran early Sunday, inserting itself into Israel’s effort to destroy Iran’s nuclear programme in a risky gambit to weaken a longtime foe.

The decision to directly involve the U.S. comes after more than a week of strikes by Israel on Iran that have moved to systematically eradicate the country’s air defenses and offensive missile capabilities, while damaging its nuclear enrichment facilities.

But U.S. and Israeli officials have said that American stealth bombers and a 30,000-pound (13,600-kilogram) bunker buster bomb they alone can carry offered the best chance of destroying heavily fortified sites connected to the Iranian nuclear programme buried deep underground.

President Donald Trump announced the strikes Saturday night. Iran’s state-run IRNA news agency reported that attacks targeted the country’s Fordo, Isfahan and Natanz nuclear sites.

Iran’s foreign minister said Iran reserves the right to retaliate.