Global supplies of oil are likely to suffer a “major jolt” following Saturday’s attack by a swarm of explosive drones on the world’s biggest oil processing plant in Saudia Arabia.

Major fires engulfed the Abqaiq processing facility and the Khurais oil field after the attack, for which Houthi rebels in Yemen claimed responsibility. They said they launched 10 drones with “intelligence cooperation from people inside Saudi Arabia”, according to the rebel-run Saba news agency. The rebels’ spokesman Yahya Saree said their operations “will expand and would be more painful as long as the Saudi regime continues its aggression and blockade” on Yemen, he said.The fires are now under control at both facilities, Saudi state media said.

Saudi Arabia’s oil fields and pipeline have been the target of rebel attacks over the past year, often using single drones, but analysts said this appeared to be the biggest and most successful to date.

The attack has raised tensions in the Gulf. Houthi rebels are assisted by Iran, which has developed sophisticated drones. But US secretary of state Mike Pompeo said last night there was no evidence the strike came from Yemen and accused Iran of launching an “unprecedented attack on the world’s energy supply”.

Abqaiq, run by state-owned firm Aramco, is described as the world’s most important processing centre, where crude from several of the country’s largest oil fields is sent before being shipped for export.

The attack reduced production by five million barrels a day – nearly half the kingdom’s output and 5% of global production – according to unnamed Saudi oil ministry sources quoted by the Reuters news agency last night. The reduction will go on for at least 48 hours reports said.

“Abqaiq is the heart of the system; it just had a heart attack,” said Roger Diwan, oil consultant at IHS Markit. “We just don’t know the severity.”

Saudi Arabia’s crown prince Mohammed bin Salman was called by President Donald Trump after the attack to express US support for Saudi security, the Saudi foreign ministry said. Andrew Murrison, the British foreign office minister responsible for the Middle East, called on the Houthis to stop threatening civilian areas and Saudi commercial infrastructure.

Robert McNally, of the US-based Rapidan Energy Group, said: “Abqaiq is perhaps the most critical facility in the world for oil supply. Oil prices will jump on this. If disruption to production is prolonged, a Strategic Petrol Reserves release from International Energy Agency members seems both likely and sensible. If anything, the risk of tit-for-tat regional escalation, which pushes oil prices even higher, has just gone up significantly.”

The IEA said it was “monitoring the situation closely”. A spokesman added: “We are in contact with Saudi authorities as well as major producer and consumer nations. For now, markets are well supplied.”