A court in Tajikistan has sentenced two leaders of the Central Asian nation's banned Islamic opposition party to life imprisonment over an alleged attempted coup.

The Supreme Court on Thursday also sentenced another 12 top members of the Islamic Revival Party to jail terms of between two and 28 years at the end of a closed-doors trial that has been condemned by rights activists and the international community.

Before it was banned last year, the party represented the only popular political group in the former Soviet nation opposed to President Emomali Rakhmon's rule.

A constitutional referendum held last month opened the way for Rakhmon to serve indefinitely as president of the impoverished and corruption-ridden country.