Yemen's Shia militia has sent reinforcements to the south, security sources said Monday, amid warnings the Arabian Peninsula country is on the brink of civil war.

The militia, known as Houthis, clashed with local Sunni tribes as they approached the main southern city of Aden, where President Abedrabbo Mansour Hadi took refuge after fleeing the capital last month.

On Sunday the militia seized the airport and a nearby military base in Taez, Yemen's third-largest city which is just 180 kilometres (110 miles) north of Aden and seen as a strategic entry point to Hadi's southern refuge.

They have since moved south toward Aden but two convoys were forced to turn back after overnight clashes with tribesmen, local officials and security sources said.

It was not immediately clear how many Houthis or tribesmen may have been killed or wounded in the clashes near Al-Abd, about 40 kilometres (25 miles) from Taez, and Al-Maqatara, about 80 kilometres (50 miles) from the city.

The Houthis on Sunday also sent some 5,000 militiamen and more than 80 tanks to an area of neighbouring Ibb province that is about 30 kilometres (20 miles) northeast of Taez, local and military sources said.

The reinforcements took over schools in the area and set them up as barracks, the sources said.

Militia chief Abdulmalik al-Houthi in a televised speech on Sunday called for his supporters to mobilise for an offensive in the south, condemning Hadi as "a puppet in the hands of forces of evil".

The impoverished country has descended into chaos in recent months after the Houthis, reportedly backed by Iran, seized control of the capital and forced Hadi to flee.

Unrest has mounted, including suicide bombings claimed by the Islamic State group that killed 142 people in Sanaa on Friday.