Tajikistan blocked local access to Facebook and two Russian-language sites that published an article critical of its long-serving president on Saturday, representatives of two Internet providers said.

The shutdown was ordered by the state-run communications service, the local Internet providers told Reuters, requesting anonymity. Users who tried to access Facebook or the two websites, which published a story critical of President Imomali Rakhmon, were automatically re-directed to the home page of their provider.

Tighter Internet controls echo measures taken by other ex-Soviet, Central Asian republics, where authoritarian rulers are wary of the role social media played in revolutions in the Arab world and mass protests in Russia.

Government opponents in Tunisia and Egypt used Twitter, Facebook and other platforms to run rings around censors and organize protests that eventually toppled their leaders.

This morning, we carried out the instruction of the communications service and blocked the sites facebook.com, tjknews.com and zvezda.ru, said one of the providers. We could not refuse to carry out this instruction.

The communications service was not available for comment. Government officials directed all questions about the shutdown to the service.

Rakhmon has ruled Tajikistan, a mountainous country of 7.5 million people bordering Afghanistan and China, for two decades. Though media operate with less restrictions than in neighboring Uzbekistan, journalists have been detained in recent months.

Authorities have also launched a crackdown on religious groups and imprisoned more than 150 people in the last two years on charges of extremism and attempting to subvert the constitution.

Facebook's popularity has soared in Tajikistan. Membership of the social networking website doubled there last year to 26,000 people. Several Facebook groups openly discuss politics and some users have been critical of the authorities.

Russia-based zvezda.ru had published an article on Friday entitled: 'Tajikistan on the eve of a revolution'. Local news site tjknews.com republished the article.

Access to microblogging site Twitter appeared unaffected.

Tajikistan is the most impoverished of 15 former Soviet republics. Its economy relies heavily on exports of aluminum and cotton, as well as remittances from around 1 million migrant laborers, most of them young men living in Russia.

Rakhmon must stand again for election by November 2013. Victory would secure seven more years as president of the mainly Muslim country.

(Writing by Robin Paxton; Editing by Ben Harding)