Two drones struck the US embassy in the Saudi capital Riyadh early on March 3, causing a fire and "minor material damage" to the compound, the Saudi Defence Ministry said.

"The official spokesman for the Ministry of Defence, Major General Turki Al-Maliki, announced that the US Embassy in Riyadh was attacked by two drones, according to initial assessments. The attack resulted in a small fire and minor material damage to the building," state news media agency SPA reported.

Black smoke was seen rising over Riyadh's Diplomatic Quarter following the attack. Saudi air defences intercepted four drones targeting the area, a source close to the Saudi military told AFP earlier.

The embassy building was empty at the time and there were no reported casualties, according to two people familiar with the matter cited, with video showing large plumes of smoke coming from the compound, according to video seen by IntelliNews. 

Separately, a fuel tank at Oman's Duqm commercial port was hit in a drone attack, causing limited material damage and no casualties, the state-run Oman News Agency reported.

The strikes on diplomatic and commercial targets in Gulf states mark a widening of Iran's retaliatory campaign, which has targeted US military assets and interests across Saudi Arabia, the UAE, Bahrain and Qatar since the joint US-Israeli operation against Iran on February 28.

Earlier, US President Donald Trump told NewsNation that the American response to the embassy attack and the killing of several US service members in the wider conflict "would soon be made clear," saying: "You'll find out soon."

The attacks are placing growing pressure on Persian Gulf governments that host US military bases and assets, with the GCC holding an emergency foreign ministers meeting on March 1, condemning what it called Iran's "flagrant and unjustified" strikes on member states.