Yemen’s Iran-aligned Houthis said on Friday they had attacked Saudi energy and military sites with 18 armed drones, and the kingdom’s energy ministry reported that a projectile had struck a petroleum products distribution station, causing a fire.

The Saudi-led coalition which is battling the Houthi group said late on Thursday it had intercepted several drones aimed at Saudi Arabia. The attacks came days after Riyadh presented a peace initiative that includes a nationwide truce in Yemen as the war enters its seventh year.

The Houthis, who control Yemen’s capital and most populous areas, have stepped up drone and missile attacks on Saudi targets in recent weeks. Meanwhile, Riyadh faces increasing pressure from Washington to end the war, after new US President Joe Biden withdrew his predecessor Donald Trump’s support for the conflict.

Houthi military spokesman Yahya Sarea said the group had targeted facilities of state oil giant Saudi Aramco in Ras al-Tanura, Rabigh, Yanbu and Jazan. He said they also targeted King Abdelaziz military base in Dammam and military sites in Najran and Asir.

"We are prepared to carry out stronger and harsher military attacks in the coming period,” he said on Twitter.

Aramco, when contacted by Reuters on Friday, said it would comment at the earliest opportunity.

The Saudi energy ministry said that at 9 p.m. on Thursday a projectile had struck a petroleum products distribution station in Jazan that caused a fire in a tank. There were no casualties.

It said such attacks on vital installations target the stability of global energy supplies.

The Saudi defense ministry said on Friday the kingdom would take deterrent actions to protect oil exports.

“These attacks confirm the terrorist Houthi militia’s rejection of all political efforts to end the crisis,” defense ministry spokesman Colonel Turki al-Malki, who also speaks for the Saudi-led coalition, said in a statement.

The Houthis are pushing for the full lifting of a sea and air blockade on areas the group controls. In addition to stepping up drone and missile attacks on Saudi Arabia, they are pressing a ground offensive to seize Yemen’s gas-rich Marib region.

The coalition has responded with air strikes on Houthi military sites.

United States envoy Tim Lenderking was due to travel to the region again on Thursday to press for the ceasefire plan. The State Department said he would meet Houthi leaders.

The war has killed tens of thousands of people and caused what the United Nations says is the world’s largest humanitarian crisis, with millions facing famine.

The Saudi-led coalition intervened in Yemen in March 2015 after the Houthis ousted the government in the capital Sanaa.

The Houthis, who now control most of northern Yemen, deny Saudi accusations they are puppets of Iran and say they are fighting a corrupt system and foreign aggression.