The Iran-backed Houthi militia in Yemen was engaged in fierce battles against fighters backed by Saudi Arabia on Sunday, as the group steps up its push to expand its territory, according to local officials. The ground fighting is the latest sign of how the war between Saudi Arabia and the Houthis that resumed in July is escalating.

On Saturday, the armed group said it had launched missiles and drones at Riyadh, the Saudi capital, and at oil facilities, in retaliation for hundreds of Saudi airstrikes and other attacks inside Yemen. On Sunday, battles were raging in al-Wazi'iyah, al-Madaribah and al-Arah, mountainous territory in the southwest of Yemen, according to Abdul Basit al-Baher, an army officer with the Saudi-backed government. If the Houthis gain control of the areas, they could cut off the city of Taiz from the southern capital of Aden and lay siege to Saudi-backed forces in Taiz, he added.

Fierce battles have also taken place in recent days around Kahboub, a mountainous territory that overlooks the Bab al-Mandab Strait, a choke point for international shipping. The waterway became a critical trade route for Saudi Arabia after Iran effectively blockaded the Strait of Hormuz in the Persian Gulf. Saudi officials have not responded to repeated requests for comment on the war.

President Trump rebuffed an appeal this month by Crown Prince Mohammed bin Salman of Saudi Arabia for increased military support to battle the Houthis. Around the same time, the Houthis seized control of Yemen's entire Red Sea coastline. "The Houthis are trying to consolidate gains on the West Coast and to take additional territory, particularly in Taiz and Marib governorates," said April Alley, a Yemen expert and senior fellow at The Washington Institute.