Shiite rebels in Yemen, backed by supporters of former President Ali Abdullah Saleh, have taken control of the country's third-largest city, Taiz and its airport, according to multiple media reports.

Fighters from a Shiite group, known as Houthis, were seen arriving at the city's airport in military uniform, while dozens of tanks and military vehicles could be seen heading towards Taiz, eyewitnesses told the BBC.

The city's supposed capture comes just one day after the Houthi rebels called for a general mobilization against forces loyal to the embattled current president, Abed Rabbo Mansour Hadi, who was previously placed under house arrest by rebel forces in the capital, Sana'a, the Associated Press reported.

Yemeni anti-aircraft guns on Sunday opened fire at an unidentified plane flying over Hadi's compound in Aden and appeared to force it away, witnesses cited by Reuters said.

A spokesperson for the Yemen embassy in Washington said the country was teetering on the brink of full-scale war, Al Jazeera reported.

"I hate to say this, but I'm hearing the loud and clear beating of the drums of war in Yemen," Mohammed al-Basha wrote on Twitter.

The alleged fall of Taiz comes as the U.S. pulled its military forces -- which amounted to about 100 special operations troops -- out out the country, citing security concerns.

Yemen has been increasingly beset by factional violence in recent months, with groups including al-Qaeda, the Islamic State group and the Houthis involved in violence.

The Houthis, who are backed by Iran's Shiite government, took over the capital, Sana'a, in Sep. 2014, and control at least nine of Yemen's 21 provinces, USA Today reported. The rebels' success against the U.S.-backed government threatens a key U.S. anti-terrorism partner in the region.

The UN Security Council is scheduled to hold an emergency meeting on the security situation in Yemen on Sunday.