The United States and the European Union called on Belarus on Sunday to release and rehabilitate all political prisoners and voiced concern about deteriorating rights conditions in the year since a crackdown in the former Soviet state.

Over the past 12 months, the Belarusian authorities have imprisoned peaceful demonstrators, suppressed non-violent protests, and worked to silence independent voices, said a joint statement by U.S. Secretary of State Hillary Clinton and EU High Representative Catherine Ashton.

They voiced concern about credible reports of degrading and inhumane treatment of political prisoners caught up in the crackdown by the government of President Alexander Lukashenko.

We reiterate our call for all political prisoners to be immediately released and rehabilitated, said the statement, which came two days after the European Union imposed sanctions on two Belarusian officials involved in prosecuting human rights activist Ales Belyatsky.

Clinton and Ashton called for the release of Belyatsky, who was jailed for 4-1/2 years for tax evasion in November, as well as presidential candidates Andrei Sannikau and Mikalai Statkevich.

We also express grave concern over new laws that will further restrict citizens' fundamental freedoms of assembly, association and expression and that target support to civil society, said the statement.

Improvement in Belarus' relations with the United States and the European Union is conditional on progress by Minsk in the respect for fundamental human rights, the rule of law and democratic principles, it said.

(Reporting By Paul Eckert)