MOSCOW (Reuters) - Russia has banned a U.S. environmental lobby group from operating in the country after labeling it an “undesirable” organization, the 15th foreign group to fall foul of legislation brought in under President Vladimir Putin four years ago.

The Justice Ministry added the group, Pacific Environment, to a list of banned organizations on Tuesday evening after prosecutors last week said it posed a threat to state security.

The San Francisco-based group, which could not immediately be reached for comment, campaigns with local partners to protect the environment in Siberia and the Far East from fossil fuel extraction, mining and illegal logging, according to its website.

Rights and other lobby groups that receive foreign funding have come under pressure in Russia since Putin signed into law legislation in 2015, banning “undesirable” organizations from operating in the country.

Relations between the United States and Russia are at post-Cold War lows and were buffeted this week by a new round of U.S. sanctions that came into effect on Monday.