MOSCOW: Police detained more than 4,400 people across Russia and blocked off the centre of Moscow on Sunday in a massive clampdown on protests demanding the release of jailed Kremlin critic Alexei Navalny.

Thousands of protesters defied government warnings to rally from Vladivostok to Saint Petersburg in a second weekend of mass demonstrations over the arrest of President Vladimir Putin's most prominent opponent.

Navalny was detained at a Moscow airport in mid-January after flying back to Russia from Germany where he was recovering from an August poisoning he blames on the Kremlin. The 44-year-old anti-corruption campaigner is being held in a Moscow detention centre and faces years of potential jail time in several different criminal cases, despite calls from Western governments for his release. In moves not seen in years in Moscow, authorities locked down the centre of the capital Sunday, with hundreds of police lining the streets, central Metro stations closed and the movements of pedestrians restricted.

Protesters who had hoped to gather outside the headquarters of the FSB security service were instead scattered to various parts of the city as organisers made last-minute changes in locations.

AFP journalists saw dozens of protesters detained and taken into police vans.

Several thousand were seen marching throughout the city centre, but it was unclear amid the chaos how many people took part in the demonstration. Independent monitor OVD-Info said at least 4,407 people had been detained across the country, after reporting more than 4,000 detentions during similar protests on January 23.