The Islamic State group claimed responsibility for a deadly shooting at a military parade in southwestern Iran on Saturday, its propaganda agency Amaq said.
Citing a security source, Amaq said: "Islamic State fighters attacked a gathering of Iranian forces in the city of Ahvaz in southern Iran".
The statement was posted on Amaq accounts on on messaging application Telegram.
At least 24 people were killed in the attack, including a young girl as well as troops, Iran's state media reported.
Three of the attackers died at the scene while a fourth was arrested and later succumbed to his wounds, armed forces spokesman Brigadier General Abolfazl Shekarchi said.
Foreign Minister Mohammad Javad Zarif said earlier he held a US ally in the region responsible.
"Terrorists recruited, trained, armed & paid by a foreign regime have attacked Ahvaz," Zarif said in a tweet, adding: "Iran holds regional terror sponsors and their US masters accountable for such attacks".
Ahvaz lies in Khuzestan, a province bordering Iraq that has a large ethnic Arab community and has seen separatist violence in the past, which Iran has blamed on its regional rivals.