The investigative newspaper has faced multiple attacks over the years, including the murder of journalist Anna Politkovskaya.
Investigative Russian newspaper Novaya Gazeta said Monday that an unidentified chemical substance was found at the entrance of its offices in Moscow.
"In the morning, a chemical attack was carried out on the building where our editorial office is located," said Novaya Gazeta editor in chief Dmitry Muratov in a statement.
"We can't walk between floors or go to the street," he added.
The chemical substance is currently under analysis by Russia's security service FSB, Muratov said.
The incident comes as three NGOs filed a lawsuit on Monday against Russian mercenary group Wagner over the torture and killing of a detainee in Syria. Muratov noted in the statement that the case was "based on our articles".
In 2019, Novaya Gazeta published an investigation into the assassination. Images showed Russian-speaking men hitting their victim with a hammer and then dismembering him, eventually spraying him with gasoline and setting his body on fire.
The newspaper also published on Monday an investigation into abuses committed in Chechnya. The autonomous republic in the Caucasus region is run by authoritarian leader Ramzan Kadyrov.
Novaya Gazeta and its journalists have suffered numerous attacks since the newspaper was created in 1993.
In 2006, journalist Anna Politkovskaya was gunned down in the entrance hall of her apartment block in Moscow.
She was investigating Russian President Vladimir Putin and the Kremlin's tactics in Chechnya.
In 2018, a funeral wreath and a severed goat's head were left outside the investigative newspaper's offices with a note reading: "To Novaya Gazeta's chief editor."
The newspaper is owned by its editorial staff, business tycoon Alexander Lebedev and former Soviet leader Mikhail Gorbachev.