Yemen's Shiite Huthi militia on Saturday formed a "security commission", consolidating its grip on power after a takeover denounced by opponents as a "coup" and condemned by the international community.
The declaration was followed by a blast outside the Huthi-controlled presidential palace, and a protest by thousands of people on the streets of Sanaa, witnesses said.
Gunmen loyal to the Shiite Muslim militia, which is also known as Ansarullah, fired into the air to disperse the demonstrators in the capital and detained 17 of them.
It was a second successive day of anti-Huthi protests in Sanaa and other cities after the militia dissolved parliament and created a "presidential council" Friday in a move it said was to fill a power vacuum.
The Shiite militia overran Sanaa in September and seized the presidential palace and key government buildings last month, prompting President Abedrabbo Mansour Hadi and Prime Minister Khalid Bahah to tender their resignations.
In its announcement on Saturday, the Huthi movement said Hadi's defence minister, General Mahmud al-Subaihi, would chair its newly formed security commission, which also included the outgoing interior minister.
The security commission "will lead the country's affairs until the establishment of a presidential council," the Huthis said in a statement published by official Saba news agency, which they seized in January.
But Subaihi's entourage reacted to the appointment with mistrust, because the general is considered close to Hadi, and suggested he was forced into accepting the post.
"We lost contact with him and we are concerned for his life," Abdel Aziz Mansour, an aide to the general, told AFP.
The Huthis' move on Friday to tighten its grip on power triggered angry condemnation from powerful Sunni Muslim tribes, which branded it a "coup".
Huthi television channel Al-Massira said militia chief Abdel Malek al-Huthi would address supporters later Saturday during celebrations in Sanaa's northern suburbs.
On Friday the Huthis said they would set up a national council of 551 members to replace the legislature in the violence-wracked country, a key US ally in the fight against Al-Qaeda.
The five-member presidential council would form a transitional government to govern for two years, they announced in a "constitutional declaration".
The announcement came after a Wednesday deadline set by the militia for political parties to resolve the crisis passed with no agreement, and also included the creation of a "revolutionary council".
UN envoy Jamal Benomar, who has been striving to seek a negotiated solution to the crisis, was back in Sanaa on Saturday and expected to meet members of the revolutionary council, Saba reported.
Friday's declaration by the Huthis bore the signature of Mohammad Ali al-Huthi and described him as "the president of the revolutionary council".
The council "will take all the necessary measures to defend the sovereignty of the nation, ensure its stability and security and guarantee the rights of citizens," the declaration said.
The Huthis celebrated with fireworks in Sanaa and in the northern stronghold of Saada as protests erupted in the capital, second city Aden and third city Taez.
Influential tribal leaders in the oil-rich eastern province of Marib said they "rejected the authors of this coup".
A US official, speaking in Munich after Secretary of State John Kerry met leaders of Yemen's Gulf neighbours, said the United States and the Gulf Cooperation Council "don't agree" with the Huthi "presidential council".
Liu Jieyi, president of the UN Security Council, said the body's 15 members were ready to "take further steps" if negotiations to halt the unrest were not resumed "immediately".
Yemen, which is also fighting an Al-Qaeda insurgency, has been riven by instability since the Arab Spring-inspired uprising that forced autocratic president Ali Abdullah Saleh from power in 2012.
There has been no immediate reaction from Saleh to the latest Huthi announcements, although he has been accused of backing the militia, as has Shiite-dominated Iran which also has not reacted.