“We announce that the Geneva 2 conference is not, nor will it ever be our people's choice,” the groups said in a statement read out by the Suqour al-Sham (Falcons of the Levant) Brigade chief, Ahmed Eissa al-Sheikh, in a video posted online on Sunday.
The militant groups also warned that anyone who attends the Geneva peace talks would be committing “treason, and ... would have to answer for it before our courts.”
The joint declaration comes as divisions are deepening among foreign-sponsored Syrian opposition groups over their participation in the Geneva 2 conference planned for November.
The so-called Syrian National Coalition is to meet on November 9 to decide whether to take part in the peace talks.
Meanwhile, UN-Arab League Special Envoy to Syria Lakhdar Brahimi is preparing to travel to Damascus on Monday as part of a regional tour to muster support for the Geneva meeting.
On Saturday, he said in Tehran that Iran's participation in the Geneva 2 talks is "necessary."
Brahimi had visited Turkey, Jordan, Iraq, Egypt, Kuwait, Oman and Qatar before travelling to Iran in order to attract their support for the talks.
The war in Syria started in March 2011, when pro-reform protests turned into a massive insurgency following intervention of western and regional states.
According to the United Nations, more than 100,000 people have been killed and millions displaced in the violence.
SHI/SHI