More explosions have been heard in the Saudi capital, with suspicions once again falling on the Houthi rebels from Yemen.

The conflict between Saudi Arabia and the Iran-backed militant group continues to escalate, with both sides trading attacks.

It has led to questions for the Trump administration, which looks increasingly mired in a war with Iran that it does not know how to exit.

The sight of smoke rising from some of Saudi Arabia's most sensitive facilities has rattled the region and global markets.

The Houthis claimed attacks against Riyadh's King Khalid International Airport as well as oil facilities in the eastern city of Dhahran, home to the headquarters of Saudi Arabia's national oil company.

They also said they struck a refinery in Riyadh.

The Houthis said the strikes were retaliation for "treacherous Saudi aggression" against the rebel-held Yemeni capital of Sanaa and other areas.

Recent attacks have highlighted Saudi Arabia's struggle to intercept Houthi missiles and drones - as well as the kingdom's efforts to press allies like the US for more support.

Experts say that trying to shoot down all the missiles and drones is impossible - especially now that the country is reportedly running low on interceptors.

The Houthis have a large arsenal capable of striking targets well over 1,000 miles away, with some warheads able to change direction mid-flight.

Meanwhile, Saudi forces have been striking areas of Yemen that are held by the Houthis.

The conflict between Saudi Arabia and the Houthis reignited this year after the rebels blamed the Saudis for a strike on the airport in Sanaa.

On Wednesday, the Houthi-run health ministry said two people were killed and two others wounded in an airstrike on an oil facility near Ras Isa port. The ministry blamed Saudi Arabia.

The Saudi-led coalition also attacked an oil facility in Sanaa.