MOSCOW — Russia"s opposition on Saturday held its first major protest since President Vladimir Putin in January announced plans which critics fear will help him stay in power after his mandate ends in 2024. The rally marks five years since the assassination of opposition politician Boris Nemtsov but its organizers want the event to also send a message to Putin after he proposed major constitutional changes. Organisers, including the country"s most prominent opposition leader Alexei Navalny, called for a mass turnout. Many see the protest as a test of society"s willingness to push back against Putin"s apparent plans to extend his grip on power. "The Kremlin is going to look at how many people attend the Nemtsov March," said Navalny. In January, Putin unleashed a political storm, proposing an overhaul of the constitution, the first changes to the basic law since 1993. Analysts see the plan as beginning preparations for succession when Putin"s fourth presidential term ends in 2024, while the opposition says the Kremlin strongman wants to remain leader for life. Putin first came to power as prime minister in 1999 under Boris Yeltsin before becoming president in 2000. He served the maximum two consecutive terms between 2000 and 2008 before a four-year stint as prime minister. He returned to the Kremlin in 2012. The demonstration is also the first major street action by the opposition since police violently broke up a series of anti-government protests last summer. Authorities however authorized a 30,000-strong rally after dozens of prominent figures, including writers and scientists, petitioned the city hall. Smaller rallies are expected in a number of cities including St. Petersburg. Russia is planning to hold a public vote on the constitutional amendments on April 22. More than 48,000 people have so far signed a petition against "a constitutional coup and usurpation of power". According to the Levada Center, an independent pollster, a quarter of Russians will back the constitutional proposals, while 56 percent said they were not sure why the changes were needed. "An inspiration to all" Forty-four percent also said Putin should quit power in 2024, while 45 percent said he should stay. Viktoria Popova, an artist, said she would join Saturday"s march but admitted she found the constitutional proposals confusing. "Honestly, I don"t understand what"s happening and I am not in a position to figure it out," she told AFP. Nemtsov — one of Putin"s most vocal critics and a former deputy prime minister in the Yeltsin government — was shot and killed near the Kremlin on Feb. 27, 2015. In 2017, a court found a former security force officer from Chechnya guilty of his murder and sentenced him to 20 years in prison. Four other men were found guilty of involvement in the killing. But Nemtsov"s family and allies insist the authorities have failed to bring the masterminds to justice. On Thursday, Putin decorated a senator who critics say has links to one of his assassination"s alleged organizers, sparking dismay among members of the opposition. The European Union and the United States said Nemtsov"s murder should be fully investigated. "Boris Nemtsov remains an inspiration to all who strive for justice, democracy, and a government accountable to the people," US Embassy spokeswoman Rebecca Ross wrote on Twitter. Protesters will also urge authorities to release Russia"s political prisoners. A number of people were jailed after tens of thousands rallied in Moscow last summer to demand fair elections, in the biggest upsurge of protests in the country for over half a decade. This month a Russian court also jailed seven people for between six and 18 years on terror charges. Their supporters say the seven are victims of a security services conspiracy and were tortured to incriminate themselves in a throwback to Stalin-era practices. — AFP