A little-known group claiming to have links to Al-Qaeda on Tuesday claimed responsibility for the deadly metro bombing in St. Petersburg, Russia, earlier this month.
The Imam Shamil Battalion said the attack was carried out on the orders of Al-Qaeda leader Ayman al-Zawahiri, according to the BBC.
Its statement has been circulated by high-profile Al-Qaeda supporters on the Telegram messaging app.
The attack in St. Petersburg killed 16 people, including the suicide bomber.
Russian officials later said Akbarzhon Jalilov, a Russian citizen born in Kyrgyzstan, detonated a bomb between two metro stations in the city.
The Imam Shamil Battalion statement said the bombing was revenge for Russian military actions in Muslim countries such as Syria and Libya, as well as the Muslim region of Chechnya in Russia's North Caucasus.
The statement warned that more attacks were being planned, but the authenticity of the claim has not been independently verified.
Russian authorities have so far made no comment.