The United Arab Emirates said a drone strike had triggered a fire near its nuclear power station on Sunday, calling the incident a "dangerous escalation".
Officials are investigating the source of the strike. The country's defence ministry said three drones had entered the UAE from the "western border direction".
While two were intercepted, the third drone struck an electrical generator "outside the inner perimeter" of the Barakah Nuclear Power Plant in Abu Dhabi, sparking a fire.
No injuries were reported and there was no impact on radiological safety levels, local authorities said.
The UAE's foreign ministry called the strike an "unacceptable act of aggression" and said it had the right to respond to any hostilities.
It added that "the targeting of peaceful nuclear energy facilities is a flagrant violation of international law, the UN charter, and the principles of humanitarian law".
The country's defence ministry meanwhile said it would "firmly confront any attempts to undermine the country's security".
Officials have not said from where the drone was launched. The UAE has previously accused Iran of being behind attacks on its energy and economic infrastructure since war broke out in the region in February.
The Abu Dhabi Media Office said the fire "broke out in an electric generator" and confirmed precautionary measures had been taken at the plant, which is operating as normal.
The UN's nuclear watchdog said it was monitoring the situation closely and that its director general Rafael Grossi expressed "grave concern" about the incident.
Grossi said "military activity that threatens nuclear safety is unacceptable", according to a statement shared by the International Atomic Energy Agency on X, and called for "maximum military restraint".
Also on Sunday, Saudi Arabia's defence ministry said it had intercepted and destroyed three drones which had entered its airspace from Iraq.
Tehran began launching strikes across the region in retaliation to the US and Israel's attacks against Iran on February 28.
It has since accused the UAE and other American allies in the Gulf of allowing the US to carry out attacks from their territory.
At the same time, the UAE has denied Iranian claims that it has actively carried out attacks of its own.
The US and Iran agreed a ceasefire in April, but sporadic exchanges of fire have continued.
President Donald Trump said the truce was on "massive life support" on Monday, after rejecting Iran's demands to end the war and reopen the Strait of Hormuz - a crucial shipping lane which has been effectively closed since the war began.
