The United States has charged four Belarusian government officials with aircraft piracy, for diverting a Ryanair flight last May to arrest a dissident journalist who was on board.

Belarusian Roman Protasevich and his Russian girlfriend Sofia Sapega were arrested in Minsk after the plane - which was en-route to Lithuania - was forced to land in the Belarusian capital.

The defendants were charged in a one-count indictment alleging conspiracy to commit aircraft piracy on a plane where a U.S. national was aboard, violating U.S. federal law.

Four U.S. citizens were among the approximately 132 passengers and crew members aboard the flight.

The charges provide one of the most detailed accounts yet of how a fake bomb threat was allegedly used to force Ryanair flight 4978 to land in Minsk.

The diversion was directed by the head of Belarus' state aviation authority, Leonid Mikalaevich Churo, and a state security official identified as FNU LNU, according to prosecutors, who used acronyms for unknown first and last names.

Also named were Churo's deputy, Oleg Kazyuchits, and FNU LNU's superior, Andrey Anatolievich LNU.

U.S. prosecutors said controllers were barred from alerting neighboring Ukraine of the alleged fake threat while the flight was in their airspace - ensuring the plane would diverted to Minsk.

After the forced landing, Belarusian officials then began a cover-up, prosecutors said, which included creating false incident reports with one showing that the fake bomb threat was received at about the time the flight entered Belarusian airspace.

President Alexander Lukashenko has denied the charges, and was quoted on Friday by state news agency Belta as saying that

Belarus did not intercept, re-route or force the landing of a Ryanair plane last year.

The charge against the defendants carries a maximum sentence of life in prison and a mandatory minimum sentence of 20 years behind bars.

Belarus already has faced a wave of sanctions, including travel bans and asset freezes, from the United States, the European Union, Britain and Canada over the diverted flight.