More than a dozen pro-Iran fighters arrested by elite Iraqi forces were released Monday and the case against them dropped, their group's spokesman told Agence France-Presse (AFP).

Members of Kataeb Hezbollah were arrested late Thursday for planning a rocket attack on Baghdad's Green Zone, where the U.S. and other embassies, as well as state buildings, are located.

"The judge ordered their release due to a lack of evidence. The arrests shouldn't have happened," Kataeb Hezbollah's military spokesman Jaafar al-Husseini told AFP.

The raid in which the fighters were arrested was the most brazen action by Iraqi forces against a major Iran-backed militia group in years and targeted the Kataib Hezbollah faction, which U.S. officials have accused of firing rockets at bases hosting U.S. troops and other facilities in Iraq.

Since October, nearly three dozen attacks have targeted American interests in Iraq, including a range of military bases, the U.S. embassy in Baghdad and U.S. oil companies. They have killed Iraqi, U.S. and U.K. military personnel. The U.S. has blamed Kataib Hezbollah for the attacks and has retaliated twice, in both cases after rockets killed U.S. military personnel stationed at Iraqi bases. Washington has pressured Baghdad to take tougher action against the group.