The attack on the Saudi city of Najran comes as Iran announced quadrupling its uranium-enrichment production capacity amid tensions with the US, escalating security concerns in the Middle East.
Yemen's Houthi rebels said on Tuesday they launched a bomb-laden drone into Saudi Arabia, targeting an airport with a military base, an attack acknowledged by the kingdom as Mideast tensions remain high between Iran and the United States.
It was not clear if there were any injuries or what the extent of damage was.
In the drone attack, the Houthis' Al Masirah satellite news channel said early Tuesday they targeted the airport in Najran with a Qasef-2K drone, striking an "arms depot."
Najran, 840 kilometres (525 miles) southwest of Riyadh, lies on the Saudi-Yemen border and has repeatedly been targeted by the Iran-allied Houthis.
On Monday, Houthis denied Saudi media reports that it had fired a ballistic missile toward Mecca, Islam’s holiest site, at a time of heightened tensions between Tehran and Gulf Arab states allied to Washington.
Saudi Arabia and the UAE are leading a Western-backed coalition of Sunni Muslim states that intervened in Yemen in 2015 to try to restore the internationally recognised government ousted from power in Sanaa by the Houthis in late 2014.
The conflict has since killed more than 10,000 people – most of them civilians – and left more than 60,000 wounded, according to the World Health Organization. Other estimates suggest over 40,000 fatalities.
The war has pushed 14 million Yemenis to the brink of famine in what the United Nations describes as the world's worst humanitarian crisis.
'Had tried to target'
A statement earlier on the state-run Saudi Press Agency quoted Saudi-led coalition spokesman Col Turki al Maliki as saying the Houthis "had tried to target" a civilian site in Najran, without elaborating.
Al Maliki warned there would be a "strong deterrent" to such attacks and described the Houthis as the "terrorist militias of Iran."
Similar Houthi attacks in the past have sparked rounds of Saudi-led air strikes on Yemen, which have been widely criticised internationally for killing civilians.
Civilian airports throughout the Middle East often host military bases.
The New York Times last year reported that American intelligence analysts were based in Najran, assisting the Saudis and a US Army Green Berets deployment on the border.
The Pentagon and the US military's Central Command did not immediately respond to requests for comment.
Iran's nuclear programme and escalating violence
Last week, the Houthis launched a coordinated drone attack on a Saudi oil pipeline amid heightened tensions between Iran and the US.
Earlier this month, officials in the United Arab Emirates alleged that four oil tankers were sabotaged and US diplomats relayed a warning that commercial airlines could be misidentified by Iran and attacked, something dismissed by Tehran.
The attack on the Saudi city of Najran came as Iran announced it has quadrupled its uranium-enrichment production capacity amid tensions with the US, underscored by an exchange of threats and taunts on Monday on Twitter between President Donald Trump and Iran's foreign minister.
Iranian nuclear officials made a point to stress that the uranium would be enriched only to the 3.67 percent limit set under the 2015 nuclear deal with world powers, making it usable for a power plant but far below what's needed for an atomic weapon.
But by increasing production, Iran soon will exceed the stockpile limitations set by the accord.
Tehran has set a July 7 deadline for Europe to set new terms for the deal, or it will enrich closer to weapons-grade levels in a Middle East already on edge.
The Trump administration has deployed bombers and an aircraft carrier to the Persian Gulf over still-unspecified threats from Iran.
Iran's enrichment announcement came after journalists visiting the country's underground enrichment facility in Natanz were given a statement by an unidentified nuclear scientist who wore a surgical cap and a mask.
His outfit wasn't explained, although Israel is suspected of targeting Iranian nuclear scientists.
The state-run IRNA news agency quoted Behrouz Kamalvandi, the spokesman of the Atomic Energy Organization of Iran, as confirming the capacity had been quadrupled.
He said Iran took this step because the US had ended a programme allowing it to exchange enriched uranium with Russia for unprocessed yellowcake uranium, as well as ending the sale of heavy water to Oman.
Heavy water helps cool reactors producing plutonium that can be used in nuclear weapons.
Kamalvandi said Iran had informed the International Atomic Energy Agency of the development. The Vienna-based UN nuclear watchdog did not respond to a request for comment. Tehran long has insisted it does not seek nuclear weapons, though the West fears its programme could allow it to build them.
If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!— Donald J. Trump (@realDonaldTrump) May 19, 2019
Trump's war on Iran
Before Iran's announcement, Trump tweeted:
Trump's remarks reflect what has been a strategy of alternating tough talk with more conciliatory statements he says is aimed at keeping Iran guessing at the administration's intentions. He also has said he hopes Iran calls him and engages in negotiations.
He described his approach in a speech Friday, saying, "It's probably a good thing because they're saying, 'Man, I don't know where these people are coming from,' right?"
But while Trump's approach of flattery and threats has become a hallmark of his foreign policy, the risks have only grown in dealing with Iran, where mistrust between Tehran and Washington stretches four decades. While both sides say they don't seek war, many worry any miscalculation could spiral out of control.
Iranian Foreign Minister Javad Zarif responded by tweeting that Trump had been "goaded" into "genocidal taunts."
Zarif referenced both Alexander the Great and Genghis Khan as two historical leaders that Persia outlasted.
"Iranians have stood tall for a millennia while aggressors all gone," he wrote. "Try respect - it works!"
Zarif also used the hashtag #NeverThreatenAnIranian, a reference to a comment he made during intense negotiations for the 2015 nuclear accord.