MOSCOW (AP) — Russian authorities on Thursday outlawed the publisher of an investigative media outlet and listed its journalists as “foreign agents,” the latest move in a series of steps to raise pressure on independent media.

The Proekt online outlet has published investigative reports exposing alleged corruption and abuses by top officials and tycoons close to Russian President Vladimir Putin.

The Prosecutor General's office outlawed Project Media Inc. the U.S.-based publisher of Proekt, as an “undesirable” organization, charging that it “poses a threat to the foundation of the constitutional order and security of the Russian Federation.”

Russian authorities also designated Proekt's chief editor Roman Badanin and several of his journalists “foreign agents.”

The government already has outlawed more than 30 groups under a 2015 law that made membership in “undesirable” organizations a criminal offense.

Another law obliges non-governmental organizations and some individuals who receive foreign funding and engage in activities loosely described as political to register as “foreign agents.” The designation comes with additional government scrutiny and has a strong pejorative connotation that could discredit those that receive it.

Last month, police searched the apartments of Proekt's chief editor Roman Badanin and several of its journalists just as the outlet was preparing to release an investigation into Interior Minister Vladimir Kolokoltsev and his alleged wealth. Proekt published it immediately after the raids.

Authorities said the searches were conducted under a defamation case over a 2017 documentary about a St. Petersburg businessman with alleged ties to organized crime.

In recent months, Russian authorities have increased pressure on independent news media, designating two popular independent outlets, Meduza and VTimes, as “foreign agents.” VTimes has shut down after that, while Meduza has launched a crowd-funding campaign.

Russia also has used the law on “foreign agents” to levy heavy fines on U.S.-funded Radio Free Europe/Radio Liberty for failing to identify its material as produced by “foreign agents.” The broadcaster has asked the European Court of Human Rights to intervene.

Russian authorities have raised the heat on the opposition and independent media ahead of September's parliamentary election, widely seen as an important part of Putin’s efforts to cement his rule ahead of the 2024 presidential election. The 68-year-old Russian president, who has been in power for more than two decades, pushed through constitutional changes last year that would potentially allow him to hold onto power until 2036.

Last month, a Moscow court outlawed organizations founded by imprisoned Russian opposition leader Alexei Navalny by labeling them extremist. The ruling barred people associated with Navalny’s Foundation for Fighting Corruption and his sprawling regional network from seeking public office. Many of Navalny’s allies had hoped to run for parliamentary seats in the Sept. 19 election.

Vladimir Isachenkov, The Associated Press