The US believes Iranian commandos were involved in a deadly attack on a compound of dissidents inside Iraq in September, reflecting Tehran’s growing power in Iraq in the wake of the US’ withdrawal from the country, according to Foreign Policy magazine.

The attack on a base called Camp Ashraf killed at least 50 members of the Mujahedeen-e Khalq (MEK), which had disarmed at the request of the US military after the American invasion of Iraq. MEK leaders have said Iraqi security forces carried out the attack, but Baghdad has long denied the charge.

US intelligence officials have now concluded that a small number of Iranian paramilitaries from its Islamic Revolution Guards Corps helped plan and direct the assault on the camp. Gunmen from two of Tehran’s Iraqi-based proxies, Kitab Hezbollah and Asaib Ahl al-Haq, then carried out the actual attack.