Hundreds of armed Shiite rebels staged sit-ins Tuesday on the outskirts of the Yemeni capital Sanaa, where protest leaders have demanded the government meet their demands within 72 hours.
Activists in the Ansarullah, or Huthi, rebellion erected dozens of tents at the western edge of Sanaa.
Guarded by armed men, rebels were also putting up similar camps in the north and south of the city, AFP journalists reported.
Around 5,000 men arrived in the capital from Saada province, a traditional stronghold of the Ansarullah rebellion.
Rebel leader Abdul Malik Huthi on Sunday ordered his followers to march on Sanaa to bring about "the fall of the government, which has failed".
He set the government a deadline of Friday before the launch of other forms of "lawful" protest action, without elaborating.
The protests have been fuelled by a steep increase in petrol prices that has had a major impact on household budgets in the impoverished country.
Tens of thousands of Shiite rebels demonstrated in Sanaa city centre on Monday.
The programme of protests will go on until Friday and "we will not yield", one rebel told AFP.
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"President Abdrabuh Mansur Hadi should listen to the voice of the people, or we will overthrow this corrupt government which has starved the people," the militant said at one of the sit-ins.
Hadi met senior colleagues on Tuesday and warned the protesters against any breach of security.
He accused the rebels of "irresponsible" actions and proposed holding a "national emergency" conference to preserve a political transition process started after the ouster of his predecessor, Ali Abdullah Saleh, in early 2012 following a year of nationwide protests.
Hadi warned of "firm and legal action" if the protests ran out of control.
Security forces have stepped up their presence at the western edge of Sanaa.
"We have been charged with ensuring safety and preventing armed groups from entering Sanaa," Abdulghani Tajeddin, commander of a local unit, told AFP.
"We will confront any armed group seeking to harm the country's security and stability."
The face-off could degenerate if the rebels seek to escalate their action, political sources said.
"We won't accept the status quo that the Huthis want to impose on us by force of arms," warned Mohamed al-Sabri, head of a political coalition including Islamist party Al-Islah, a Sunni bloc.
"If they make an attempt to enter Sanaa... it will be suicide for them," he said.
Ansarullah controls Saada province in northern Yemen and is suspected of wanting to broaden its sphere of influence in a future federal state, potentially comprising six provinces.
Huthi forces reached just outside Sanaa in July when they took over the city of Amran, although they later agreed to withdraw.