Russian courts have sentenced hundreds of people who were caught laying flowers for Russian opposition leader and renowned Putin critic Alexei Navalny, who was found dead in prison earlier this week.

Navalny, 47, fell unconscious and died last Friday after a walk at the remote Arctic penal colony where he was serving a three-decade sentence, the prison service said.

Mourners have left hundreds of flowers at the Solovetsky Stone monument in Moscow, with US Ambassador Lynne Tracy and Britain’s Nigel Casey among those seen paying their respects.

More than 400 people have been detained in Russia while paying tribute to Navalny, who had remained vocal in his unrelenting criticism of the Kremlin even after surviving a nerve agent poisoning and receiving multiple prison terms.

Details of rulings published by the city’s court service over the weekend showed 154 people had been given jail time of up to 14 days for violating Russia’s strict anti-protest laws.

Rights groups and independent media outlets reported a handful of similar sentences in other cities across the country.

There are still few details of why he died, but prison authorities have said he suffered ‘sudden death syndrome’. However, Navalny’s allies and many world leaders have blamed his death on Putin and his government.

Police over the weekend arrested hundreds of Russians in dozens of cities who came to lay flowers and light candles in his honour at memorials to victims of Stalin-era repressions.

Anti-Kremlin demonstrations or public shows of opposition to the regime are effectively illegal in Russia under strict military censorship rules and laws against unapproved rallies.

Police and men in plain clothes patrolled sites in dozens of Russian cities where people had gathered to commemorate Navalny over the weekend.

More than 200 arrests were made in St Petersburg, Russia’s second-largest city, the group said.

Among those detained there was Grigory Mikhnov-Voitenko, a priest of the Apostolic Orthodox Church – a religious group independent of the Russian Orthodox Church – who announced plans on social media to hold a memorial service for Navalny and was arrested on Saturday morning outside his home.

He was charged with organizing a rally and placed in a police holding cell, but was later taken to hospital after suffering a stroke, OVD-Info reported.

Courts in St Petersburg have ordered 42 of those detained on Friday to serve from one to six days in jail, while nine others were fined, court officials said.

In Moscow, at least six people were ordered to serve 15 days in jail, according to OVD-Info. One person was also jailed in the southern city of Krasnodar and two more in the city of Bryansk, the group said.