"Twenty-one soldiers of the state national security committee Alfa special task force and seven army soldiers died," one military source said.

The helicopter went down in the Rasht region, 180 km east of Dushanbe, capital of the Central Asian country.

Tajik armed forces have been engaged in a combat operation in the area, after an assault on a military convoy on Sept 19 that killed 28 soldiers and wounded 12.

The press office of the National Guards, which operated the Russian-built MI-8 helicopter, confirmed only the deaths of four soldiers and would not comment on a larger death toll.

Technical failure was believed to have caused the crash, a spokesperson for the guards said, without giving details.

The Rasht region has been the stronghold of Islamic insurgency since the bloodshed of Tajikistan's civil war in the 1990s, when Islamist guerillas fought against the authoritarian regime of Emomali Rakhmon.

Reuters