Yemen’s Houthi movement said on Friday it had launched attacks with drones on a military air base and oil facility in Saudi Arabia, the latest indication that diplomacy to end the six year conflict has so far failed to take hold.

The Houthi military spokesman said on Twitter the group had targeted the King Khalid air base with two drones and had struck a facility of Saudi Arabia’s oil company Aramco with a drone in the southwestern Saudi city of Jizan. He later said the Houthis had launched a third strike on the air base.

Earlier on Friday, Saudi state television quoted the Saudi-led coalition fighting in Yemen as saying it had intercepted two explosives-laden drones fired by the Houthis at the city of Khamis Mushait, where the air base is located. There was no immediate confirmation of the Jizan attack or the third attack on the air base.

The military coalition led by Saudi Arabia, which intervened in Yemen against the Iran-aligned Houthis in 2015 after the Houthis captured the capital Sanaa, says it intercepts the majority of Houthi missile and drone attacks.

The Houthi movement, which holds most of north Yemen, has kept up cross-border attacks on Saudi Arabia and a ground offensive in Yemen’s Marib region at a time the United States and the United Nations are pushing for a ceasefire agreement.

Riyadh has proposed a truce, but the Houthis reject the offer, saying they want the full lifting of a sea and air blockade which allows the Saudi-led coalition to restrict imports into Yemen.

The conflict, seen in the region as a proxy war between Saudi Arabia and Iran, has killed tens of thousands of people and pushed millions the brink of famine in what the United Nations calls the world’s worst humanitarian crisis.

The battle for gas-rich Marib is complicating U.S. efforts to reach a ceasefire needed to end the war and secure a foreign policy win for President Joe Biden.