The US, UK and Ukraine may have been behind last Friday’s terrorist attack on a concert venue in a suburb of Moscow, which claimed lives of 139 people and left around 200 injured, according to the head of Russia’s Federal Security Service (FSB).

Aleksandr Bortnikov told reporters on Tuesday that the authorities are currently trying to establish the identity of everyone involved in the attack, both inside and outside Russia.

When asked whether the US, Britain and Ukraine could be behind the terrorist attack, the FSB chief responded: “We think that this is so. In any case, we are now talking about the information that we have. This is general information, but they [investigators] also have concrete results.”

Bortnikov’s statement to the media follows a meeting of the expanded board of the Prosecutor General’s Office of Russia. The FSB director told reporters that the intelligence service will do everything necessary to identify the direct organizers and sponsors of the terrorist attack.

On the evening of March 22, a group of men armed with assault rifles attacked the Crocus City Hall music venue in the Moscow suburb of Krasnogorsk, just before a concert by the rock band Picnic was due to start. The 7,500-capacity venue was almost full at the time of the attack. The terrorists killed guards, shot concert-goers on sight, then started a fire that quickly spread throughout the building.

At least 139 people, including three children, were killed in the attack, the chair of the Russian Investigative Committee, Aleksandr Bastrykin, reported on Monday. Around 200 people were injured, according to the latest data.

After the attack, Russian security services detained 11 people connected to the incident, including those believed to be the gunmen who carried out the attack.

Moscow’s Basmanny Court has since arrested seven other suspects who are accused of helping organize the terrorist attack.