Yemen's Iran-backed Houthis have advanced to within 80 km (50 miles) of Aden, the main stronghold and temporary capital of the country's internationally recognized government, four military sources told Reuters on Monday.
The advance brings the Houthis closer to Aden than at any point since the early months of the war in 2015, when they briefly entered the city before being driven out.
The latest offensive has opened a volatile new front in the wider US-Israeli war with Iran, drawing both the Houthis and Saudi Arabia deeper into the regional conflict.
The Houthis have escalated their attacks on Saudi Arabia, which backs Yemen's government, while the Saudi-led coalition has responded by stepping up strikes on Houthi positions in Yemen.
The violence has shattered a 2022 UN-brokered truce that had largely halted major attacks in a war that began in 2014, when the Houthis drove the government from Sanaa.
Houthi advance threatens main road linking Aden to Taiz
The Houthi push threatens strategic positions along the main road linking Aden with the besieged city of Taiz, a vital artery for southwestern Yemen.
It follows a broader offensive that began in September, when the Houthis swept down Yemen's Red Sea coast and seized territory along the Bab el-Mandeb Strait, one of the world's most important shipping lanes and a key route for Saudi oil exports to Asia.
The advance gives the Houthis a chance to outflank government forces along the mountain range overlooking the Bab el-Mandeb Strait, the military sources said. Government troops had expelled Houthi fighters from the area only weeks ago.
Houthi attacks on Aden, the government's temporary capital since 2015, have also intensified in recent weeks. The group struck Aden airport on Wednesday after warning people to evacuate, while the presidential palace was also hit in October.
Houthis, Yemeni government forces clash throughout Monday
Fighting between the Houthis and government forces was underway on Monday at a military camp at the entrance to Tur al-Bahah district, one of the main approaches to Aden. The camp is about 50 km from the provincial capital of Lahj and 80 km from Aden.
The Houthis launched their assault on government positions in Al-Maqatirah three days ago and have since taken the whole district, the sources said. The mountainous area overlooks the road linking Taiz to Aden. The Houthis forced government troops to retreat toward Tur al-Bahah, they said.
Yemen's information minister did not immediately respond to a request for comment.
Houthi official Hamid Rizq posted a video, which Reuters could not immediately verify, of what he said were the group's fighters entering Souq al-Rabouh in Maqatirah district.
That route has been the last remaining link between government-held territory and Taiz during the war.
Taiz, Yemen's third-largest city, has been encircled since early October, when the Houthis cut its main road south to Aden. The siege has displaced more than 100,000 people and caused shortages of food, fuel and medicine.