Shiite Muslim rebels surged Wednesday toward the southern Yemen port of Aden, where President Abed Rabbu Mansour Hadi took refuge last month after the nation's capital was overrun.
The Houthi rebels also claimed to have seized a major air base, Al-Anad, and circulated photos of the Yemeni defense minister and the base's commander, both of whom were reportedly injured in fighting there.
The president's whereabouts were not immediately known, but a Houthi-controlled TV channel announced a $20-million bounty for his capture, and his Aden compound came under aerial bombardment.
Foreign Minister Riadh Yassin said Hadi was still in Aden and was overseeing the city's defense from an undisclosed safe location. But the Associated Press, citing unnamed Yemeni security and port officials, later reported that Hadi has left the country by sea.
Yemen appeared to be descending into all-out civil war, and one with the potential to ignite a wider regional struggle. The Reuters news agency reported that Saudi Arabian troops were massing on the kingdom's border with Yemen, which sits alongside key shipping routes.
Iran, the Shiite Muslim rival of Sunni Saudi Arabia, is thought to be aiding the Houthis, and the conflict in Yemen has taken on an increasingly sectarian nature. Last week nearly 140 people were killed in bombings at two Shiite mosques in Sana, the capital.
After pitched battles in the province of Lahej, just north of Aden, the Houthis and their allies, backed by tanks and artillery, advanced to within a few miles of Aden, officials and witnesses said. Much of the rebels' heavy weaponry was provided by elements of the Yemen military that remained loyal to former President Ali Abdullah Saleh, who was toppled in 2012 and is a bitter opponent of Hadi.
The fighting has closed Aden's airport. Last week, passengers on an outgoing flight were forced to disembark and take shelter in the terminal as the two sides battled for control of the airport.
The struggle for Aden comes in advance of an Arab League summit. Yemen is poised to seek a military intervention by fellow Sunni Muslim states, and the Houthis appeared to be trying to gain as much ground as possible before the gathering.
In the town of Houta, the capital of Lahej province, the fighting left bodies strewn in the streets, residents reported, and people cowered indoors as gunfire rang out. The Houthis appeared to be consolidating control of the town's southern outskirts, closest to Aden.
The Houthis, mainly adherents of the minority Shiite Muslim Zaidi sect, have been battling Hadi loyalists as well as the Yemen affiliate of Al Qaeda. The Houthis seized Sana in September and at the time expressed willingness to engage in power-sharing talks. Over the weekend, however, they seized the central city of Taiz.
The ongoing fighting has shuttered nearly all Western and Arab embassies, and forced a pullout of U.S. intelligence and military personnel. In recent years, Yemen had been an important ally in the American drone war against Al Qaeda, whose affiliate in the country is considered one of the network's most dangerous.
Special correspondent Al-Alayaa reported from Sana and Times staff writer King from Cairo.