The incident followed a similar strike on the US Embassy in Kuwait, which has since been closed until further notice.
Iran expanded its targets on Tuesday by striking the United States Embassy in Riyadh, even as Washington, DC began pulling staff out of several West Asian countries amid an escalating conflict that has disrupted global oil and gas supplies, shipping lanes and air travel.
Saudi Arabia's Defence Ministry said two drones hit the US diplomatic compound in the capital, causing a 'limited fire'.
The embassy urged Americans to avoid the facility.
The incident followed a similar strike on the US Embassy in Kuwait, which has since been closed until further notice.
The US State Department ordered the evacuation of non-emergency personnel and family members from Kuwait, Bahrain, Iraq, Qatar, Jordan and the UAE. Washington has also advised its citizens to leave more than a dozen countries in the region, although widespread airspace closures have left many stranded.
The conflict entered its fourth day with Israel deploying additional ground troops into southern Lebanon and fresh explosions reported in Tehran.
US President Donald Trump said the war could last four to five weeks and indicated the US was prepared for a longer campaign, without ruling out the possibility of ground troops.
The initial US-Israeli strikes killed Iran's Supreme Leader Ali Khamenei, after which Trump urged Iranians to overthrow their government.
However, senior US officials later clarified that regime change was not an official objective.
According to the Iranian Red Crescent Society, at least 787 people have been killed in Iran since the strikes began.
In Israel, 11 people have died in Iranian missile attacks.
Hezbollah attacks and Israeli retaliatory strikes have left 52 dead in Lebanon.
The US military has confirmed six American service members killed, while additional casualties have been reported in the United Arab Emirates, Kuwait and Bahrain.
The widening hostilities have intensified concerns of a prolonged regional conflict with significant global economic repercussions.