Law enforcement officers detain an opposition supporter during a rally in Moscow, Russia, March 26, 2017. REUTERS/Maxim Shemetov

GENEVA (Reuters) - United Nations human rights experts called on Russia on Wednesday to release peaceful protesters arrested across the country at the weekend and to annul any sentences already handed down.

In a joint statement, the independent experts said that Russia had a legal obligation to protect people exercising their right to fundamental freedoms of peaceful assembly, opinion and expression.

Up to 1,000 demonstrators who took to the streets following allegations of corruption against Prime Minister Dmitry Medvedev were arrested and a number of them were sentenced to imprisonment and fines, they said.

“We call on the authorities to release immediately all protesters still being detained, and to quash the sentences imposed on them,” said the U.N. special rapporteurs on the rights of peaceful assembly, opinion and human rights defenders and the chairman of the U.N. working group on arbitrary detention.

“Freedom of peaceful assembly is a right, not a privilege, and as such its exercise should not be subject to prior authorization by officials,” they said.

Kremlin critic Alexei Navalny was handed a 15-day jail sentence on Monday for his part in a big anti-government protest in Moscow on Sunday which buoyed the liberal opposition’s morale a year before the country’s presidential election.

Navalny, who will appeal the court’s verdict, was found guilty of disobeying a police officer at the Moscow protest. He was also fined for organizing the protest, which the authorities said was illegal.

Genuine elections cannot be achieved if fundamental rights to freedoms of peaceful assembly, opinion and expression are curtailed, the U.N. experts said.

“The coming elections will be irreparably tainted if individuals are not allowed to exercise these basic rights without fear of harassment or retaliation,” they said.