Former Yemeni President Ali Abdullah Saleh's supporters battled Iran-aligned Houthis for a fourth day on Saturday in the capital Sanaa, residents said, in a widening rift that could affect the course of a more than 2-1/2 year civil war.
The two groups have been allies in fighting a Saudi-led coalition that intervened in Yemen's civil war in 2015 aiming to restore the internationally recognised government of President Abd-Rabbu Mansour Hadi after the Houthis forced him into exile.
The clashes underscore the complex situation in Yemen, one of the poorest countries in the Middle East, where a proxy war between the Iran-aligned Houthis and the Saudi-backed Hadi has caused one of the worst humanitarian catastrophes in recent times.
Residents described heavy fighting on the streets of Hadda, a residential district in southern Sanaa where many of Saleh's relatives, including his nephew Tareq, live.
They said explosions and gunfire were being heard all over the area. The streets were deserted except from fighters from both sides.
There was no immediate word on casualties.
The fighting resumed after a lull of several hours brought about by mediation efforts that sought to resolve the dispute.
Saleh's General People's Congress (GPC) party, accused the Houthis of failing to honour the truce and said in a statement on its website that the Houthis bear responsibility for dragging the country into a civil war.
It also called on supporters, including tribal fighters, to "defend themselves, their country, their revolution and their republic..."
The GPC appealed to the army and security forces to remain neutral in the conflict.
The Houthis' Ansarullah group, in a statement issued on its Twitter account, described the clashes as "regrettable" and said
"It is happening in coordination with it," referring to the Saudi-led coalition.
The fighting began on Wednesday when Saleh's GPC party accused the Houthis of breaking into the city's main mosque complex and firing RPGs and grenades.
Both sides reported that at least 16 people have been killed in the fighting since Wednesday.
Yemen's civil war has killed more than 10,000 people since 2015, displaced more than two million people, caused a cholera outbreak infecting nearly one million people and put the country on the brink of famine.