The Iranian military launched a ballistic missile attack at 2am on Monday morning on a site it described as the headquarters of “takfiri terrorists” in eastern Syria, the semi-official Fars news agency reported.

The term ‘takfiri’ was an apparent reference to the Sunni extremist group Islamic State, which still holds pockets of territory in eastern Syria and which last month claimed responsibility for a deadly shooting attack in southwestern Iran.

The missiles were fired from western Iran and traveled the length of Iraq to reach targets in the Albu Kamal region of Syria, a distance of approximately 570 kilometers (350 miles), Fars reported.

“The missiles were of Zolfaqar and Qiam classes with ranges of respectively 750km and 800km,” the news agency said, adding that “a few minutes after the missile strikes, seven IRGC (Islamic Revolutionary Guards Corps) drones targeted the terrorists’ positions in the region.”

The Syrian Observatory for Human Rights, a key tracker of attacks and casualties over the course of the conflict, said that explosions were heard in the Albu Kamal vicinity, which is home to Islamic State bases. But no information was available immediately on casualties.

The strike came in stated retaliation for a September 22 shooting attack on a military parade in Iran’s southwestern city of Ahvaz, which killed 26 people and left dozens of others wounded.

The Revolutionary Guards earlier blamed the attack on ethnic Arab separatists and accused neighboring Saudi Arabia of fueling the movement.

This is the second time Iran has fired missiles into Syria in response to an attack on its soil. In June 2017 the Revolutionary Guards launched a missile strike against IS targets in Syria in response to a double bombing in Tehran claimed by the group.