Yemen's rival political factions have resumed UN-brokered talks with Houthi fighters, three days after the group seized power in a coup.
However, the Nasserite party suspended its participation, denouncing the Houthi takeover.
Among those represented at Monday's meeting were the General People's Congress (GPC) and the Mushtarak (Joint Meeting Parties), a coalition made up of the Islah party, the Yemeni Socialist party, Hizb Al-Haq, the Unionist party, and the Popular Forces Union party.
Abdullah Nooman, the Nasserite party chief, said his party would "not return to the table of negotiations," charging that the Houthis were insisting on holding talks based on the "constitutional declaration" under which they took over the government on Friday.
Under the declaration, the Houthis dissolved parliament and announced the formation of a transitional "presidential council" which will act as a government for an interim period of two years.
Al Jazeera's Jamal Elshayyal, reporting from Taiz, said the Nasserites, a Leftist-Socialist party, had decided to withdraw after some of its demands were not met.
"They had demands that some of their members abducted by the Houthis be released," he said.
"And more significiantly, they were against a new decree issued by the Ministry of Interior, under the control of the Houthis, that prevents any form of protest without prior agreement."
Elshayyal also said that the Nasserites had claimed that a Houthi leader at the talks had threatened the life of one of their leaders.
Our correspondent said the Houthis main political rivals, the Islah party, were still "on the fence," and while they were continuing to to take part in negotiations, they were demanding that Jamal Benomar, the UN envoy to Yemen, take a tougher line on the Houthi takeover.
Benomar hailed Monday's resumption of talks, saying they took place "in a constructive atmosphere characterised by mutual respect, even though animated at the outset, which is not an unusual occurrence in consultations of this nature"
He said the parties had agreed to reconvene on Tuesday to continue discussing pending issues.
The Houthis, who have controlled the capital since September last year, dissolved parliament on Friday and replaced the president with Mohammed Ali al-Houthi, a cousin of Houthi leader, Abdel-Malik al-Houthi.
The group, who are accused of being backed by Iran, have vowed to defend the coup, calling it a "glorious revolution" that has "broken the shackles of injustice and corruption".
The Houthis hail from the northern region of Saada and champion the interests of the Zaidi community, who make up a fifth of Yemen's 25 million population.
Source: Al Jazeera