Kathmandu. Saudi Arabia has launched an investigation into why its air defense system failed to stop the deadly Houthi attack on the capital Riyadh airport.

At least 13 people were killed and more than 300 wounded in missiles and drone attacks by Iran-backed Yemeni Houthi rebels, regional officials said Monday.

Two regional officials, who spoke on condition of anonymity because they were not authorized to comment publicly, said preliminary investigations suggested the Houthi rebels fired several drones and then attacked Riyadh’s King Khalid International Airport with cruise and ballistic missiles.

The Houthi rebels are said to have ballistic missiles and advanced systems that can change direction during flights. Such weapons can challenge the air defense systems used by Saudi Arabia, including the Patriot.

The investigation will also look into why Saudi air defence systems failed to provide early warning about missiles and drones that had traveled more than 1,000 km (2000 miles) into Riyadh, officials said.

The latest of the Houthi attacks targeting several airports in Saudi Arabia over the past week has exposed the weaknesses in the country’s air defense system. It also indicates that the Middle East conflict, which has been expanding since the US and Israel launched a war against Iran more than seven months ago, has reached a more perilous point.

The Saudi-led coalition said it had intercepted and destroyed two sets of ballistic missiles fired toward Riyadh on Monday. At least three explosions were heard in the capital on Monday night. Civil defense officials then said the threat was over for the time being.

The Houthi rebels claimed to have targeted King Khalid International Airport on Monday. They have also warned international airlines that all airports in Saudi Arabia are unsafe, except for the Muslim holy cities of Mecca and Medina.