Rival protest leaders at the talks - held at a heavily guarded military facility in the capital - were seen being taken away by the army although it was unclear whether they had been formally detained.
The long-running political crisis broadly pits a Bangkok-based royalist elite and its backers against the billionaire family of former premier Thaksin Shinawatra.
Thaksin, a former tycoon-turned-populist politician, was ousted by the military in a coup in 2006 but still enjoys strong support, particularly in rural northern Thailand.
His sister Yingluck Shinawatra was dismissed as prime minister earlier this month in a controversial court ruling after months of protests seeking her overthrow.
Her supporters have warned of possible civil war if opposition demonstrators achieve their goal of seeing an unelected interim premier take power to oversee vaguely defined reforms widely seen as a bid to cripple the Thaksin family's political power.
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