A photo released by Greenpeace shows Michael Kreindlin, a Greenpeace Russia staff member, after being beaten by attackers in southern Russia. (Maria Vasileva/AP)

  Masked men carrying pistols, knives and truncheons stormed a Greenpeace camp site and severely beat volunteer firefighters in southern Russian on Friday, the environmentalist group said, leaving one activist with a broken nose and another with fractured ribs.

The reason for the assault wasn’t clear. But Greenpeace Russia has been at odds with Russian officials over a variety of issues, including recent claims that Russia’s regional governments were underreporting the size of local forest fires by as much as 80 percent to portray the situation as under control.

Greenpeace deploys volunteer firefighters and runs fire fighting training in many regions. 

The attack capped 24 hours of harassment by apparent patriotic vigilantes in the Krasnodar region, an area near the Black Sea, where Greenpeace firefighters had traveled to help put out local grass fires. They had already been confronted by men who identified themselves as Cossacks, socially conservative, pro-Kremlin activists who claim they are descendants of Czarist-era horsemen.

“The attackers climbed through a fence” surrounding a temporary Greenpeace camp in the region, the head of Greenpeace Russia’s firefighting project, Grigory Kuksin, said in a statement.

He said the attackers had “truncheons, knives, pistols” and also damaged cars and slashed tents.

They said that if we don’t leave here before morning, then no one would find us, that we should go 'to our America,'" Kuksin added.

Greenpeace posted a photo of the bloodstained face of Mikhail Kreindlin, a member of the firefighting team who suffered a broken nose, and said that the activists were seeking a safe place and medical attention.

While fighting forest fires may seem an apolitical task, environmental activism can carry a serious price in Russia — particularly when local business interests are involved.

Greenpeace’s most sensational conflict in Russia came in 2013 when a crew of 30 activists and journalists aboard the group’s ship, Arctic Sunrise, were arrested near an oil rig owned by a subsidiary of Gazprom, the Russian state energy giant, in the Pechora Sea in northwest Russia. The team aboard the ship was charged with piracy, but later pardoned after international negotiations.

Khalimat Tekeeva, a Greenpeace Russia press officer, called Friday’s attack unprecedented.

“We've never faced incidents like this: a group of people attacking a group of Greenpeace activists,” Tekeeva wrote. “We work with lots of firefighting groups in different regions in Russia and everything was okay.”

She added that the Russian firefighting authorities had “asked for our help and welcomed our trip” to the Black Sea region.

In May, a group wearing the traditional fleece hats of Cossacks assaults a group of anti-corruption activists at an airport in southern Russia.