The United States criticised Myanmar on Wednesday after the Asian country's high court upheld the sentencing of two Reuters journalists, expressing deep concern about freedom of expression and urging that the two be reunited with their families.

"Burma's Supreme Court decision yesterday to uphold the sentencing of Pulitzer-prize winning journalists Wa Lone and Kyaw Soe Oo, despite serious irregularities in the case against them, sends a profoundly negative signal about freedom of expression and the protection of journalists in Burma," the State Department said in a statement, using the country's former name.

Myanmar's top court on Tuesday rejected the appeal of the Reuters reporters, who were sentenced to seven years in jail for breaking the Official Secrets Act, in a landmark case that has raised questions about the country's transition to democracy.

The reporters' imprisonment has sparked an outcry from press freedom advocates, Western diplomats and world leaders, adding to pressure on Myanmar leader Aung San Suu Kyi, the Nobel laureate who took power in 2016 as the country made a transition to democracy from military rule.

The State Department said the United States was "deeply concerned" about the recent arrests in Myanmar of journalists, activists and others.

"We urge Burma to protect hard-earned freedoms, prevent further backsliding on recent democratic gains, and reunite these journalists with their families," it said in a statement.

Defence lawyer Than Zaw Aung said the families of the two men planned to seek a pardon from Myanmar President Win Myint.

- Reuters