At least 24 people were killed during an attack on a military parade in Iran's Ahvaz on 22 September (AFP)
Iran's Revolutionary Guards said on Monday that they had launched a missile attack on an alleged militant site in Syria in retaliation for a September attack on the Iranian city of Ahvaz.
"The headquarters of those responsible for the terrorist crime in Ahvaz was attacked a few minutes ago east of the Euphrates by several ballistic missiles fired by the aerospace branch of the Guardians of the Revolution," the Guards said on their official website.
"Based on preliminary reports, many takfiri terrorists and the leaders responsible for the terrorist crime in Ahvaz have been killed or wounded in this missile attack," the Guards added.
The term "takfiri", derived from the Arabic word for anathema, is used by the Iranian authorities to refer to Sunni Islamist militants – particularly those who call Shia Muslims apostates.
The Guards released pictures of what appeared to be missiles lighting up the night sky, leaving trails of smoke as they soared above a desert region with a rugged mountain in the background.
The Guards did not say where the missiles were launched from.
According to Iran's Fars news agency, the Guards fired Zolfaghar and Qiam missiles, with a range of 750 kilometres and 800 kilometres, respectively.
The agency said the missiles hit the Syrian desert border town of Albu Kamal on the west of the Euphrates River, in the eastern province of Deir Ezzor.
According to the Syrian Observatory for Human Rights, a Britain-based war monitor, "heavy explosions took place at dawn (Monday) in the last pocket under IS control near Albu Kamal".
Albu Kamal itself, located on the border with Iraq, is held by Syrian President Bashar al-Assad's forces and allied regional militiamen, who seized it from IS in 2007.
On 22 September, 24 people were shot dead in an attack at a military parade in Ahvaz in southwest Iran. The Islamic State group has claimed responsibility for the attack.
Iranian officials initially blamed Arab separatists backed by Gulf allies of the United States for the attack.
But on Monday, supreme leader Ayatollah Ali Khamenei appeared to link the perpetrators to Islamist groups operating in Iraq and Syria, where IS once had major strongholds.
"This cowardly act was the work of those very individuals who are rescued by the Americans whenever they are in trouble in Iraq and Syria and who are funded by the Saudis and the (United) Arab Emirates," Khamenei was quoted by his official website as saying.
Iranian President Hassan Rouhani had vowed a "crushing" response in retaliation.