US journalist Evan Gershkovich has been found guilty of espionage by a Russian court and sentenced to 16 years in a high-security penal colony, after a secretive trial decried as a "sham" by his employer, his family and the White House.

The Wall Street Journal (WSJ) reporter was first arrested last March while on a reporting trip in the city of Yekaterinburg, about 1,600km (1,000 miles) east of Moscow, by security services.

Prosecutors accused him of working for the Central Intelligence Agency (CIA), accusations Mr Gershkovich, the WSJ and the US vociferously deny.

It marks the first conviction of a US journalist for espionage in Russia since the Cold War ended more than 30 years ago.

Both sides in the trial have 15 days to appeal against the verdict, the judge said.

“This disgraceful, sham conviction comes after Evan has spent 478 days in prison, wrongfully detained, away from his family and friends, prevented from reporting, all for doing his job as a journalist,” Wall Street Journal publisher Almar Latour and Editor in Chief Emma Tucker said in a statement.

“We will continue to do everything possible to press for Evan’s release and to support his family.

“Journalism is not a crime, and we will not rest until he’s released. This must end now.”

Washington accuses Russia of holding Mr Gershkovich as a bargaining chip, to be used for a possible prisoner swap with Russian citizens in foreign jails.

But Moscow knows that the US is prepared to make swaps in order to release its own citizens, and the two countries are known to have been discussing such a swap.

Russian observers say a quick conviction could mean that an exchange is imminent. According to Russian judicial practice, an exchange generally requires a verdict to already be in place.

The trial began last month, and the last two days' proceedings had originally been scheduled for August. Prosecutors had asked for an 18-year prison sentence.

But in an unexpected move, the hearing was brought forward to Thursday, and the judge gave the verdict late on Friday afternoon.

In a charging indictment, prosecutors accused Mr Gershkovich, 32, of acting “under instructions from the CIA" to collect "secret information" about a factory that produces tanks in the Sverdlovsk region.

The reporter has consistently denied the accusations, and in a statement on Thursday the WSJ called the trial a "shameful sham" and his detention an "outrage".