Russia cracks down on the free press and outlaws Meduza, a leading independent news site.

Russian officials continued their campaign to stifle press freedom on Thursday, labeling the independent news website Meduza an “undesirable organization” and effectively outlawing its content. The move made Meduza the latest journalistic outlet to fall victim to the Kremlin’s efforts to suppress criticism.

The Russian prosecutor general’s office said that Meduza’s activities posed “a threat to the foundations of the Russian Federation’s constitutional order and national security,” according to the Interfax news agency.

Over the past year, Moscow has ramped up its attempts to control coverage of the war in Ukraine. In March, President Vladimir V. Putin signed a law effectively criminalizing any public opposition to or independent reporting about the war.

Announcements about the new law pushed some Russian independent news media outlets to shut down even before it was enacted. The Russian government has also cut off access to Facebook and to the BBC and other news sources.

“Russian authorities are showing that they will do anything to impede the work of one of the leading independent Russian-language media outlets,” Gulnoza Said, the Europe and Central Asia coordinator of the Committee to Protect Journalists, a press watchdog organization, said in a statement.

Meduza, a popular Latvia-based outlet that publishes news about Russia in both Russian and English, often reports critically on the war in Ukraine. It posts on its website and to over one million subscribers on Telegram, in Russia and elsewhere.

The website was blocked in Russia last year at the start of the war, but the new “undesirable” designation has even more far-reaching consequences. Now, anyone in Russia who goes to the site, “likes” any of its social media content or shares a link to an article could face fines or jail time.

Meduza’s editor in chief, Ivan Kolpakov, called the designation a “very bad event,” but said that “nevertheless, we were waiting for this to happen — and we tried to prepare ourselves.”

The site plans to continue to publish, although its future plans are unclear.

Even before the Ukraine invasion, Moscow had labeled Meduza a “foreign agent,” wiping out its advertising revenue and compelling it to shift to a crowdfunding model to stay in business. As a foreign agent, Meduza had to add a 24-word disclaimer about its new status to all of its Russian-language content, including social media posts. If it did not, the organization and its journalists could receive fines or jail time.

In June, the independent business news site VTimes shut down after Russia’s foreign-agent designation hurt its business and made it difficult for reporters to do their jobs. And in August, the government added TV Rain, long a top independent outlet, and the news site iStories to the foreign-agent list.

Other independent news sources have been feeling pressure from Moscow’s efforts to censor their coverage, even as they see a new urgency to provide unfiltered reporting.

Radio Free Europe/Radio Liberty, a news network originally set up as a C.I.A. operation early in the Cold War, is an example. Russia’s invasion of Ukraine last February both shook up Radio Free Europe’s operations and highlighted its mission’s importance.

Within days of the invasion, the organization suspended its operations in Russia. It had faced years of growing pressure from Moscow and had already evacuated most of its staff to Prague and other offices even before the war broke out.

Jamie Fly, the broadcaster’s president and chief executive, said his organization had long been in firefighting mode.

“The challenge we’re facing now, and the invasion of Ukraine, is just the latest iteration,” Mr. Fly said in an interview late last year. “We are increasingly getting pressure when we’re operating in these environments, and in some cases, we’re getting pushed out of countries. That’s always been a challenge for us.”

Matina Stevis-Gridneff contributed reporting.