The head of Yemen's Shiite Houthi militia threatened Saturday to take control of the oil-rich Marib province, targeted by the group since it seized the capital and central areas three months ago.
"If official authorities do not assume their responsibilities, (we) will act to support the honourable people of Marib," Abdelmalek al-Houthi said in a televised address to supporters in Sanaa.
Yemen has been dogged by instability since an uprising forced longtime strongman Ali Abdullah Saleh from power in 2012, with Houthi rebels and Al-Qaeda seeking to fill the power vacuum.
The Huthis, also known as Ansarullah, overran the capital Sanaa unopposed in September and have since advanced into mainly Sunni districts.
They have been met with fierce resistance by Al-Qaeda and Sunni tribal fighters.
Houthi accused "certain" tribesmen of wanting to hand over Marib to "Al-Qaeda and the takfiris," a reference to the Islamist Al-Islah movement that has fought alongside Al-Qaeda's Yemen franchise against the Shiite group.
On Thursday Sunni tribesmen ambushed a military convoy travelling between Marib and Sanaa and seized heavy weapons they claimed were destined for Huthi militiamen, tribal sources and witnesses said.
Three soldiers died during ensuing clashes, according to Yemen's High Security Commission, which demanded in a statement late Friday the tribesmen return the military equipment they had seized.
Almost 50 people were killed in a suicide bomb attack on a religious celebration by Huthi supporters in the mainly Sunni city of Ibb on Thursday.