Zaw Lin and Win Zaw Tun were charged with the murder of David Miller, 24, and the rape and murder of Hannah Witheridge, 23, after the tourists' battered bodies were found on the island of Koh Tao last month.
The retractions are the latest blow for Thai police who have come under widespread criticism for bungling the murder investigation amid accusations the migrants were being framed for the brutal crime.
"The suspects said they did not kill them, they were not involved in the incident, and they were physically abused," Surapong Kongchantuk, the lead lawyer for the pair, told AFP.
Prosecutors confirmed today they had received a letter from the defence team in which the pair withdrew their confession and laid out allegations of torture.
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"It doesn't matter if they confessed or denied it because the court will consider evidence from forensic tests," said prosecution lawyer Paiboon Archavanuntakun.
The murders on the normally tranquil island rocked the small community and marked a new setback for Thailand's image as a holiday haven after months of protests in Bangkok led to a coup and the imposition of martial law in May.
The parents of the migrant workers were expected to travel to Koh Samui prison on today to visit their detained sons, Surapong said.