Yemen’s Iran-aligned Houthi group on Saturday attacked two plants at the heart of Saudi Arabia’s oil industry, including the world’s biggest petroleum processing facility, in a strike that three sources said had disrupted output and exports.

Two sources close to the matter said 5 million barrels per day of crude production had been impacted — close to half of the kingdom's output or 5 per cent of global oil supply.

The pre-dawn drone attack on the Saudi Aramco facilities set off several fires, although the kingdom, the world’s largest oil exporter, later said these were brought under control.

State TV said exports were continuing, however Aramco has yet to comment since the assault, which the Houthis said involved 10 drones. Authorities have not said whether oil production or exports were affected.

The attacks occurred as Aramco accelerates plans for an initial public offering of the state oil giant to as early as this year, and follow earlier cross-border attacks on Saudi oil installations and on oil tankers in Gulf waters. Saturday’s attacks appeared to be the most brazen yet.

Saudi Arabia, leading a Sunni military coalition that intervened in Yemen in 2015 against the Houthis, has blamed regional rival Shia Iran for previous attacks, which Tehran denies. Riyadh accuses Iran of arming the Houthis, a charge denied by the group and Tehran. State-run Ekhbariya TV, citing its correspondent, said there were no casualties, but there was no official statement. A Reuters witness nearby said at least 15 ambulances were seen in the area and there was a heavy security presence around Abqaiq.

“A successful attack on Abqaiq would be akin to a massive heart attack for the oil market and global economy,” said Bob McNally, who runs Rapidan Energy Group and served in the US National Security Council during the second Gulf War in 2003.

Hours after the Houthi strike in Abqaiq, the Reuters witness said fire and smoke were visible but appeared to have been extinguished by early evening. Earlier video footage verified by Reuters showed bright flames and thick plumes of smoke. An emergency vehicle is seen rushing towards the site.

The Saudi interior ministry said Aramco industrial security teams fighting the fires had managed to control them and stop their spread.

The Saudi-led coalition launched air strikes on Yemen’s northern Saada province, a Houthi stronghold, on Saturday, a Reuters witness said. Houthi-run al Masirah TV said the warplanes targeted a military camp.

The Houthis’ military spokesman, without providing evidence, said drones hit refineries at both Saudi sites, which are over 1,000km from the Yemeni capital Sanaa, and pledged a widening of assaults on Saudi Arabia.

The chief of Iran’s elite Quds Force, Qassem Soleimani, praised the Houthis in a Twitter post. Tensions in the region have escalated in recent months after the US quit an international nuclear deal.