Thailand's junta has denied accusations of torturing suspects in a bombing investigation, as human rights groups step up their criticism of the military regime.

Lawyers for four suspects in a March 7 grenade attack outside Bangkok Criminal Court say their clients alleged they were punched and tortured with electrical shocks to try to get them to confess. The grenade caused minor damage and no casualties.

New York-based Human Rights Watch said a statement Thursday that the allegations of torture in military custody heightened concern about abuses while the country remains under martial law, imposed last May. The group also criticized military trials of dissidents.

Junta spokesman Col. Winthai Suvaree called the torture allegations false, saying they were made to discredit authorities.