MOSCOW (Reuters) - Allies of jailed Kremlin critic Alexei Navalny announced plans on Tuesday to stage the biggest anti-Kremlin street protest in modern Russian history this spring, in a new push to win the opposition’s politician’s freedom. Navalny, 44, was jailed last month for two and a half years on charges he called fabricated. He was arrested as he returned to Russia from Germany in January where he had been recovering from what doctors said was a nerve agent poisoning. Supporters staged three protests at the height of winter despite the COVID-19 pandemic to demand his release. The authorities said they were illegal and broke them up with force, detaining thousands and prompting the opposition to declare a moratorium on protests. On Tuesday, Navalny’s allies launched a political campaign with its own “Free Navalny” website and said they would announce a date for a new nationwide street protest once 500,000 people had registered to attend. “A protest with 500,000 people taking part will be the biggest in the history of modern Russia,” said Ivan Zhdanov, head of Navalny’s Anti-Corruption Foundation. Navalny’s allies are trying to encourage Russians to take part in a “smart voting” strategy at September parliamentary elections to undermine the ruling United Russia party that backs President Vladimir Putin. “You know who our biggest enemy is? No, not Putin. Putin can’t stop the wonderful Russia of the future however much he wants to. Our main enemy is indifference, apathy and apoliticism,” said Leonid Volkov, a Navalny ally. Volkov urged followers to register for the protest on the website, to mark their location on an interactive map, and to spread the word. Over 60,000 people had signed up within a matter of hours, according to the website. “We’ll hold a peaceful rally in the streets of all of Russia’s cities,” he said. Navalny has used social media to air videos alleging official corruption and carved out a following among young Russians in big cities, though he has struggled to win broad support, which his allies blame on state television propaganda. The Levada Centre, a leading pollster, in February put his overall approval among Russians at 19%, while 65% of Russians approved of Putin’s work as president. The West has demanded Russia release Navalny from jail, something Moscow has called unacceptable interference in its internal affairs. Russian authorities say they have seen no evidence that Navalny was poisoned and have suggested Navalny is a Western puppet sent back to try to destabilise the political situation in Russia.