DUSHANBE -- Tajikistan on September 16 experienced a one-hour Internet outage that coincided with an address by an exiled opposition leader in the United States that was streamed live online.

Tajikistan's State Communications Service has not given any official explanation for the outage.

The service's representative told RFE/RL on September 17 that the Internet unexpectedly stopped working at around 7:40 p.m. for ”unknown reasons” and that the operator had to switch to its backup system to bring it back after about 30 minutes.

The representative added that "specialists are working to determine the cause of the outage."

Tajik social-media users say the outage lasted for one hour, some adding that mobile phone service was also affected.

The outage occurred at exactly the time when the exiled chairman of the opposition Islamic Renaissance Party of Tajikistan (IRPT), Muhiddin Kabiri, was delivering an online address to an event organized by George Washington University in Washington, D.C.

In his address, Kabiri, who resides in an EU country, accused the authorities of barring opposition candidates from taking part in the presidential poll scheduled for October 11.

The IRPT, long an influential party with representatives in the government and parliament, was labeled a terrorist group and banned in 2015.

Dozens of IRPT officials and supporters have been prosecuted and many of them imprisoned, drawing criticism from human rights groups.

In recent years, there have been several cases when access to social networks and the websites of independent media outlets have been blocked at sensitive times.

The presidential campaign kicked off in Tajikistan on September 15.

The Central Election Commission has said that five candidates, including incumbent Emomali Rahmon, have been registered.

Many in Tajikistan expect that Rahmon will be announced as the winner again, saying that the other candidates were registered just as a facade.

The only opposition party functioning inside Tajikistan, the Social Democratic Party, said earlier that it will boycott the poll.

In Tajikistan's last presidential election, in 2013, Rahmon, who has been running the country since 1992, was reelected by a landslide with 84 percent of the vote.

None of the five presidential elections won by Rahmon has been deemed free and fair by Western election observers.