Yemen’s Iran-backed Houthi rebels said Friday they attacked Saudi Aramco in the capital Riyadh using six drones, stepping up their offensive on the kingdom’s energy and security installations.

Axar.az reports citing foreign media that the Saudi government has neither confirmed nor denied the attack and it wasn’t clear what damage was caused. While the Houthis sometimes make false claims, they often hit targets in the kingdom. The claim came on the rebel-run Al-Masirah TV.

Houthi attacks on Saudi Arabia rarely claim lives or cause extensive damage but their frequency has increased in recent months, creating unease in the Gulf, a region key to global oil production and transit.

Tensions have mounted as U.S. President Joe Biden explores rejoining a 2015 accord designed to reduce Iran’s nuclear activities. He’s also vowed to bring an end to the conflict in Yemen, which the UN says has caused the world’s worst humanitarian crisis.