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Watch: Thick black plumes of smoke rise from near Riyadh's international airport
A column of black smoke has been seen near Riyadh's international airport hours after air raid alerts were issued in the Saudi capital.
It was the first time residents had been given an alert and urged to stay indoors since a recent escalation in the conflict with Iran-backed Houthi militants in neighbouring Yemen.
A number of apparent explosions have since been heard in the capital and major problems reported at King Khalid International Airport, with the tracking website FlightRadar24 reporting long delays and cancellations.
One report suggested a fuel tank had been set on fire near the airport. There has been no official comment from Saudi authorities.
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The Saudi Civil Defence had sent out phone alerts overnight warning of potential danger in Riyadh and other regions, before issuing an all-clear on Saturday morning.
"In the direction of the airport we saw black smoke and fire," one resident told the agency.
On Friday, the Houthis announced that they had thwarted Saudi attacks on the Yemeni capital Sanaa which they said bore the hallmarks of an Islamic State operation.
Houthi military spokesman Yahya al-Sarea said Saudi Arabia had carried out 300 strikes across Yemen during the past week.
He warned the reported attacks on Sanaa would "not go unanswered".
The Houthis, who are locked in a civil war with Yemen's internationally recognised government, recently seized control of the strategic port city of Mokha and Perim Island, a gateway to a key shipping route used by the Gulf state to export to Asia and Europe.
The group said the naval blockade was in retaliation for a Saudi blockade of ports and airports in Houthi-controlled north-western Yemen.
Saudi vessels have relied on that stretch of the Red Sea for oil exports since the US and Israel's war with Iran effectively closed the Strait of Hormuz.
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