The United States has imposed new sanctions on Belarus in response to its continued incarceration of political prisoners.

The U.S. State Department said Thursday the sanctions imposed on four Belarusian companies are aimed at inducing the country's authoritarian president, Alexander Lukashenko, to release political activists, journalists and civil society representatives who were jailed December 19, following the disputed presidential election.

Mr. Lukashenko was declared the winner in the 2010 vote that was widely criticized by international observers.  He has ruled Belarus with an iron fist since 1994.

The U.S. Treasury Department said that as a result of Thursday's action, U.S. citizens are prohibited from doing business with Naftan oil refinery, Grodno Azot fertilizer manufacturer, Grodno Khimvolokno fiber manufacturer and Belshina tire factory.  It said the four firms are owned or controlled by the state-run Belneftekhim conglomerate.  

The new sanctions are in addition to the travel ban imposed earlier this year on President Lukashenko and other Belarusian officials.

President Lukashenko's office announced Thursday that he has pardoned nine participants of December 19 mass protests in central Minsk.

Human rights organization Amnesty International, in a statement Thursday, urged Belarusian authorities to release prominent human rights activist Ales Bialatski, the head of the Human Rights Center Viasna.  

The group says he was arrested August 4 on charges tax evasion. Amnesty International believes the charges are politically motivated and that Bialatski was using his personal Lithuanian bank account to support his organization's rights activities in Belarus.