An aide to Tatarstan's chief prosecutor, Ildar Mukhametzyanov, said the two men -- Ravil Gumarov and Fanis Shaikhutdinov -- were detained on March 7 and would soon be transferred to Kazan.
Shaikhutdinov and Gumarov were first arrested in 2005 and charged with blowing up a gas pipeline in the town of Bugulma.
Gumarov and a third man arrested for the Bugulma attack -- Timur Ishmuratov -- are among seven Russian citizens captured by U.S. troops in Afghanistan and released in 2004 after spending several months in Guantanamo Bay.
A jury in Tatarstan cleared them of all charges in September. But the Russian Supreme Court's Cassation Chamber later overturned the acquittal.