In a video posted on the YouTube website, three rebels wearing balaclavas and combat gear and holding automatic weapons said the Barisan Revolusi Nasional (BRN), one of several militant groups would withdraw from the talks.
"The Thai occupiers have committed betrayal, violence, lied and slandered the Pattani people," one of them said, in the video posted Tuesday and confirmed by sources close to the talks today.
Pattani is one of several provinces in the south, where some 5,700 people have been killed since the insurgency flared in 2004. Rebels also use the word to refer to the whole deep south region.
But rebel attacks began again after a few days, with local observers recording 29 deaths during Ramadan which ended yesterday.
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In the clip, rebels said Thai authorities had failed to meet the conditions of the negotiations, without detailing their complaints.
It was not possible to verify who the rebels in the clip represent. But an official involved in the talks said they were from BRN, which has shown signs of internal division recently.
"It sounds like there won't be any more talks, but actually that's not the case," the official said, requesting anonymity.
"Once the BRN is satisfied, they will continue the dialogue."
Talks between the government and representatives of the BRN began on March 28 but have so far failed to halt near-daily violence, raising questions about the rebel group's influence over increasingly violent grassroots insurgents.