"It's not entirely clear who was behind the attack, but the fact that Ansar Allah has claimed responsibility is bad enough," Griffiths said. "And whatever we will discover of the attack, it is a sure sign that Yemen seems to be moving even further away from the peace we all seek."
Griffiths warned that the attack increases the odds of conflict in the Middle East and could have dangerous consequences beyond the region.
On Saturday, Saudi Aramco's Abqaiq plant and its Khurais oil field came under drone attacks that cut the kingdom's crude output in half to around 5.7 million barrels per day.
The Houthi rebel movement in Yemen claimed responsibility for the attacks, but US officials said that intelligence indicates Iranian involvement in the incidents.
