Two activists from the Agit Russia group who allegedly installed a mock gravestone with the name Vladimir Putin on it have been detained by police in Russia's second-biggest city, St. Petersburg.

The group said on April 5 in a post on its Telegram social-network account that Andrei Zheksimbayev and Grigory Kudryavtsev were charged with violating the law on the organization of public events for placing the tombstone near the iconic St. Isaac’s Cathedral. They face up to 10 days in jail if found guilty.

The group insists the two had nothing to do with the stunt, as it was actually done by other members.

Another group called Help the Detained in St. Petersburg said the two men were detained late on April 3, the day the mock gravestone appeared in Putin's native city.

Agit Russia then published a picture of the site on the Internet and said on Twitter that it was behind the mock headstone.

The tombstone features a picture of Putin, his name, and an inscription reading, "He betrayed the people of Russia."

It also says "1952-2019" -- the former a reference to the year Putin, who has held power as Russia's president or prime minister since 1999, was born.

"We wanted to say this: Because of the antipeople laws that have been adopted, the constant lies, and the disgusting [method of] rule, Putin is dead to the citizens of Russia," the group said in a tweet with a photo of the poster in front of St. Isaac's.

The cathedral is one of the most recognizable buildings in St. Petersburg, where longtime Soviet KGB officer Putin was born, raised, and began his political career in the 1990s before his move to Moscow and his rise to the presidency.

The tweet said that St. Petersburg was "taking the baton" -- apparently a reference to similar political pranks carried out in Moscow and the city of Naberezhnye Chelny, in the Tatarstan region, in the past month.

Two activists in Naberezhnye Chelny were sentenced to jail terms of 28 days and six days in March after they put up a mock Putin gravestone there.