Rights groups have criticised Thailand for giving death sentences to five suspected militants convicted of killing four soldiers.
Pattani Provincial Court found the men guilty on Wednesday of opening fire on the soldiers while they were on patrol in the southern province July 2012.
Human Rights Watch accused Thailand of double standards, saying the army was also responsible for rights violations.
Several rebel groups are fighting for more autonomy in southern Thailand.
The country is majority Buddhist but Pattani, Yala and Narathiwat provinces are ethnically-Malay and mostly Muslim.
Separatists carry out regular attacks, usually roadside bombings or drive-by shootings, and since the conflict began in 2004 about 6,000 people have died in the three southern provinces.
The military maintains a high presence in the region, and has controversially given arms to local people to help them tackle the insurgency.
Despite repeated accusations of rights abuses by the security forces, Sunai Phasuk of Human Rights Watch told Reuters that there had never been a successful prosecution of a soldier.
"Violence does not come from the separatists alone. The security forces have their own share of responsibility," he said.
Rupert Abbott, Amnesty International's Southeast Asia research director, told AFP that the death penalty "is a human rights violation in itself and will do nothing to stem the tide of violence in Thailand's south".
"It might be tempting for the Thai authorities to think of the death penalty as a quick fix to combating insecurity, but there is no evidence whatsoever that the threat of execution acts as a particular deterrent to crime."
Peace talks with rebel groups came to a standstill when the country was plunged into a political crisis earlier this year.
The government, which took power in acoup, has pledged peace in the region.