A Shi rebel leader in Yemen warned President Abdrabuh Mansur Hadi on Friday to form a new government within 10 days or a "national salvation council" would take its place.
The Ansarullah rebels, also known as Houthis, took advantage of the lack of stability since president Ali Abdullah Saleh's 2011 overthrow to seize the capital Sanaa on September 21.
They have since extended their sphere of influence into the centre and west of the country.
Friday's warning to Hadi came as rebel leaders gathered in the capital at a meeting called by the movement's chief, Abdulmalik al-Houthi.
It was attended by Houthi supporters, the heads of allied tribes and also backers of the deposed Saleh, participants said.
"We are giving President Hadi 10 days to form a government as provided under the peace agreement" reached on September 21 or "a national salvation council will be set up", said tribal chief Sheikh Dheifallah Rassam from the northern rebel bastion of Saada province.
Participants at the meeting denounced Hadi's call last Sunday for the Houthis to "immediately pull out their armed men from all the cities and provinces (they seized) including Sanaa".
The president accused the rebels of "trying to take over the role of the state under the pretext of fighting Al-Qaeda in a bid to conquer more provinces".
On Wednesday, the rebels seized the central city of Radmah on a road linking Sanaa with the main southern city of Aden.
And an Ansarullah statement issued after Friday's meeting said "popular committees will be formed in all provinces... to control the actions of the state".
In addition to hardening their stance against Hadi, the rebels are also defying parliament which on Thursday called for the army and police to be deployed in Sanaa and other rebel-controlled areas to reestablish security.
The rebels want greater political clout in impoverished Yemen, which is located next to oil kingpin Saudi Arabia and key shipping routes in the Gulf of Aden.
Yemen is also a key US ally that has allowed Washington to conduct drone strikes against Al-Qaeda on its territory.
Under the UN-sponsored September 21 deal, the Houthis were to withdraw from Sanaa and disarm once a neutral prime minister is named.
But the agreement has not been implemented, although a new premier has been named, and the rebels remain in the capital in addition to expanding into other areas.
The rebels say they are filling the void left by the security forces and standing up to Al-Qaeda in the Arabian Peninsula, viewed by Washington as the deadliest franchise of the global extremist network.