Paris (AFP) - An attack on Saudi oil facilities at the weekend has exposed the vulnerability of the kingdom to drone strikes and underscores how traditional air defences can be breached by new low-cost technology, experts say.
Saudi Arabia is one of the world's biggest buyers of weapons and spent an estimated $65 billion on arms last year, mostly from the United States, according to the Stockholm International Peace Research Institute (SIPRI).
Its air defences include the latest radars, fighter jets such as the F-15, and Patriot missiles which are meant to intercept missiles fired from enemy territory.
But on Saturday, attacks on national energy giant Aramco's Abqaiq processing plant and the Khurais oil field knocked 5.7 million barrels per day (bpd) off production, over half of the OPEC kingpin's output.
"The Huthis' use of drones to attack Saudi Arabia has identified gaps in its air defences," Becca Wasser from the think-tank Rand Corp told AFP.
The exact type of weapon used has not been confirmed, but the Soufan Center, a security think-tank, said that 10 drones had been deployed.
Unidentified US officials have also told American media that cruise missiles might have been fired as well, and have suggested these came from Iran, which backs the Huthi rebels in Yemen to the south but denies being involved in Saturday's strikes.
"A coordinated attack like this is not something anyone can do, and not everyone can defend themselves against it," a former head of one of France's intelligence agencies told AFP on condition of anonymity.
- Growing capability -
The Huthis, a Shiite rebel group battling a Saudi-led coalition in Yemen since 2015, had already served notice several times that they were building up an arsenal of long-range weapons capable of eluding Saudi defences.
In March this year, they released footage taken from a drone that had flown over a desalination plant more than 120 kilometres (75 miles) inside Saudi airspace.
Then in May, a drone strike on a major pipeline in the oil-rich Eastern Province to the Red Sea forced it to be shut down temporarily.
In June alone, the Huthis launched at least 20 missile and drone attacks on Saudi Arabia, Iran's regional foe, some resulting in casualties and damage.
"We have witnessed a massive increase in capability on the side of the Huthis in recent years, particularly relating to ballistic missiles and drone technology," Andreas Kreig, a professor at King's College London, told AFP at the time.
The rebels showed off some of their advanced weaponry at an undisclosed location in July to mark the fifth anniversary of their offensive against the Yemeni government.
Footage distributed by the Huthis showed models of at least 15 unmanned drones and various sizes of missiles of different ranges.
The newest of these weapons were long-range cruise missiles, dubbed "Al-Quds", and explosives-laden "Sammad 3" drones that can hit targets as far as 1,500 kilometres (930 miles) away, according to the Huthis.
A spokesman for the Saudi coalition fighting in Yemen, Turki al-Maliki, told reporters Monday that "all indications are that weapons used in both attacks (at the weekend) came from Iran."
Experts say the threat from drones will continue, changing how countries defend themselves and how insurgencies invest in weapons.
"The problem is that there is not one system that enables you to handle every case, and the threat from drones is constantly evolving," a French military engineer told AFP recently.