The first arrests have been reported in Russia on a day of demonstrations across the country in support of detained opposition leader Alexei Navalny. According to civil rights activists, nearly 250 people were detained in the far east of the country. One hundred were detained in the major port of Vladivostock, the website Owd-Info reported. Videos posted online showed demonstrators being hauled into buses by police. The mostly young people were seen dancing and chanting: "Putin is a thief," and "freedom for Russia." Navalny supporters are planning to gather across the country on Sunday, despite authorities' warnings not to take part in the unauthorized action. Demonstrations are planned in more than 100 cities, the leading opposition figure's team said. Last weekend, hundreds of thousands of people took to the streets to call for Navalny's immediate release and to protest against Russian President Vladimir Putin. Rights activists estimate that 4,000 people were arrested and many were injured at the unprecedented protests. In an effort to dampen the protests planned for midday (0900 GMT), authorities have decided to close seven metro stations in the capital, Moscow, and shops, cafes and restaurants will not be allowed to open. They also took aim at Navalny's associates in recent days, with Navalny's brother Oleg, his associate Lyubov Sobol and other supporters being sentenced to two months of house arrest. Navalny returned to Russia earlier this month after receiving treatment in Germany following a near-fatal assassination attempt with the nerve agent Novichok. He was immediately detained upon his arrival in Moscow and sentenced to pretrial detention. A Russian court on Thursday confirmed his 30-day pretrial sentence, rejecting an appeal by the dissident's lawyers to set him free.