The UN Secretary-General António Guterres described the United States' bombing of three nuclear sites in Iran as a "dangerous escalation" on Saturday following eight days of deadly strikes and counter strikes between Tehran and Tel Aviv.
"I am gravely alarmed by the use of force by the United States against Iran today," said the UN chief, reiterating that there is no military solution.
"This is a dangerous escalation in a region already on the edge - and a direct threat to international peace and security."
President Donald Trump delivered a televised address to the nation from the White House at 10pm local time and said that Iran's nuclear facilities at Fordo, Natanz and Isfahan had been "totally obliterated" describing the long-range bombing raid as a "spectacular military success."
President Trump called on Iran's leadership to now "make peace" and return to negotiations over its nuclear programme or suffer a far greater wave of attacks.
Iranian authorities have yet to confirm the extent of the damage to the three sites in central Iran. Earlier in the day, Iran's foreign minister reportedly warned the US against an involvement in the conflict with Israel, which erupted on 13 June.
Deadly strikes
At least 430 Iranians are believed to have been killed during waves of strikes since then with around 3,500 injured, according to figures from the Iranian health ministry.
In Israel, 24 civilians have died in the retaliatory attacks according to local authorities with more than 400 missiles fired towards the country, according to Government figures.
B2 bombers were involved in the US strikes, President Trump confirmed, dropping so-called "bunker buster" bombs on the uranium enrichment site at Fordow which is buried deep inside a mountain south of the capital Tehran.
'Avoid a spiral of chaos'
In his statement, the Secretary-General reiterated his concerns voiced in the Security Council during Friday's emergency meeting on the crisis that the conflict "could rapidly get out of control - with catastrophic consequences for civilians, the region, and the world."
He called on all Member States to de-escalate the situation which threatens the stability of the Middle East and beyond, calling for everyone to uphold their obligations under the UN Charter and international law.
"At this perilous hour, it is critical to avoid a spiral of chaos," he added calling for an immediate return to negotiations between the warring parties.
"There is no military solution. The only path forward is diplomacy. The only hope is peace."
