* Yemen group says attacks Aramco plants in Abqaiq and Khurais
* Fires controlled but no official comment on possible impact
* Comes as Aramco speeds up plans for IPO, amid regional tensions
* Saudi-led coalition strikes Houthi stronghold in Yemen (Adds Twitter post by senior Iranian military commander)
By Stephen Kalin and Rania El Gamal
RIYADH, Sept 14 (Reuters) - Yemen's Iran-aligned Houthi group on Saturday attacked two Saudi Aramco plants, including the world's biggest oil processing facility, sparking fires in the latest flare up of violence in the Gulf.
Saudi Arabia said it had brought the blazes under control, without specifying whether oil production or exports were affected. State television said exports were continuing.
The drone strikes on the world's biggest oil exporter come as state oil giant Saudi Aramco has accelerated plans for an initial public offering to as early as this year, and follow earlier cross-border attacks on Saudi oil installations and on oil tankers in Gulf waters.
Saudi Arabia, leading a Sunni Muslim military coalition that intervened in Yemen in 2015 against the Houthis, has blamed regional rival Shi'ite Iran for previous attacks, which Tehran denies. Riyadh accuses Iran of arming the Houthis, a charge denied by the group and Tehran.
The extent of damage from the drone strikes in Abqaiq and Khurais provinces remains unclear. Aramco has yet to issue a statement on the pre-dawn attacks. Authorities have not reported on casualties.
Abqaiq is located 60 km (37 miles) southwest of Aramco's Dhahran headquarters. The oil processing plant handles crude from the giant Ghawar field and for export to terminals Ras Tanura - the world's biggest offshore oil loading facility - and Juaymah. It also pumps westwards across the kingdom to Red Sea export terminals.
Khurais, 190 km further southwest, contains the country's second largest oilfield.
Many Western employees of Aramco live in Abqaiq. The U.S. Embassy in Riyadh said it was unaware of any injuries to Americans from the attacks.
FIRE AND SMOKE
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 north of Saada city.
Hours after the Houthi strike in Abqaiq, a Reuters witness nearby said fire and smoke were still visible. Earlier video footage verified by Reuters showed bright flames and thick plumes of smoke rising towards the dark pre-dawn sky. An emergency vehicle is seen rushing towards the site.
The Saudi interior ministry spokesman said Aramco industrial security teams fighting the fires since 0400 (0100 GMT) had managed to control them and stop their spread. He did not identify the source of the drones but said an investigation was underway.
The Houthis' military spokesman, without providing evidence, said the attacks hit refineries at both sites, which are over 1,000 km from the Yemeni capital Sanaa, and pledged a widening of assaults on Saudi Arabia.
The chief of Iran's elite Quds Force, Qassem Soleimani, in a rare reaction to such attacks on Saudi Arabia, praised the Houthis for their resistance in a Twitter post that included the hashtag Aramco.
Tensions in the region have escalated in recent months after the United States quit an international nuclear deal and extended economic sanctions on Iran.
The Houthis hit Shaybah oilfield last month and two oil pumping stations in May. Both attacks caused fires but did not disrupt production.
The coalition has responded with air strikes on Houthi targets in Sanaa and other areas held by the group, which controls most large urban centres in Yemen.
The violence is complicating U.N.-led efforts to ease tensions between the Houthis and Riyadh to pave the way for political talks to end the war, which has killed tens of thousands of people and pushed millions to the brink of famine.
The Western-backed coalition intervened in Yemen to try to restore the internationally recognised government ousted from power in the Sanaa by the Houthis in late 2014.
The Yemen conflict is widely seen as a proxy war between Saudi Arabia and Iran. The Houthis deny being puppets of Tehran and say they are fighting a corrupt system. (Reporting by Stephen Kalin and Rania El Gamal; Additional reporting by Ahmed Tolba in Cairo, Tuqa Khalid and Parisa Hafezi in Dubai and Reuters team in Yemen; Editing by Richard Borsuk and Mark Potter)