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 were heard in the capital and major problems were reported at King Khalid International Airport, with the tracking website FlightRadar24 reporting delays and cancellations earlier in the day.

One report suggested a fuel tank had been set on fire near the airport. There has been no official comment from Saudi authorities.

An AFP news agency journalist reported that firefighters could be seen trying to extinguish the flames of a burnt-out fuel tank belonging to state oil and gas company Aramco.

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.

Residents told AFP on condition of anonymity that they had heard what sounded like a round of explosions echoing through the city after the alerts.

"I heard the alarm, then my windows shook," said a resident of northern Riyadh, 27. "It was definitely scary. I was not expecting this."

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 are locked in a civil war with Yemen's internationally recognised government, which is backed by Saudi Arabia.

They have attacked targets inside Saudi Arabia on several occasions in recent months, and said this week that they were responsible for downing a Saudi fighter jet over Yemen.

According to an unconfirmed report from AFP, quoting military sources on both sides of Yemen's civil war, fighting between the Houthis and Saudi-backed government forces claimed 48 lives on Saturday.

The Houthis said 31 of their fighters had been killed while government sources said their side had lost 17 soldiers, according to the news agency.

On Friday, the International Organization for Migration, a UN body, reported that the number of people displaced as a result of recent fighting had passed 104,796.

The Houthis 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.

On Friday, investment banking giant JP Morgan said it was struggling to predict how oil prices would be impacted by the war, telling investors in a rare note that "we simply don't know how to model the endgame".

(Source: BBC)