"We refuse to meet with Mr Staffan de Mistura if it is not on the basis of a comprehensive solution to Syria's drama through the exit of (President) Bashar al-Assad and his chief of staff, and the prosecution of war criminals," a newly-formed Aleppo revolutionary commission said.
The political and military grouping was set up yesterday at a meeting in the Turkish border town of Kilis attended by exiled coalition chief Khaled Khoja, other opposition figures and Aleppo civil society representatives.
Aleppo's opposition forces also turned down preferential treatment for their region over other areas of Syria stricken by the country's deadly conflict since 2011.
"Syria and its people are one and indivisible. The blood of our brothers in Daraa (in the south), in Ghouta (near Damascus), in Homs (central) and in other Syrian provinces are no less important than our blood in Aleppo," they said.
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He met Foreign Minister Walid Muallem and agreed to send a delegation from his Damascus office to Aleppo on a fact-finding mission, state news agency SANA said, without giving a date.
"The mission will aim to assess the situation on the ground and to ensure that, once the freeze is announced, humanitarian aid can significantly increase and to prepare arrangements to follow up on violations of the freeze," the UN said.
The Swedish-Italian diplomat "hopes to set in motion as soon as possible his project" to halt fighting in Aleppo for six weeks, said a member of his delegation.