A military parade in Iran have been attacked by gunmen with about 24 people killed and 53 others injured.
The attacked which happened at south-western city of Ahvaz had civilians as well as military men killed.
The attackers shot from a park near the parade and were wearing military uniforms, reports say.
An anti-government Arab group, Ahvaz National Resistance, and Islamic State (IS) have both claimed the attack.
"Terrorists began shooting from a long distance while inside the park, at the armed forces as well as civilians watching the parade," Brigadier General Abolfazl Shekarch, a spokesman for the Iranian armed forces told MEHR, another Iranian news agency.
Iran's foreign minister has blamed "terrorists paid by a foreign regime".
Javad Zarif added that "Iran holds regional terror sponsors and their US masters accountable"
Three of the attackers were gunned down during clashes with the security forces and one other arrested, news agencies reported.
The separatist group the Patriotic Arab Democratic Movement in Ahwaz claimed responsibility for this attack.
The group is supported by "foreign antagonists," including Saudi Arabia, IRNA said.
"The terrorists disguised as Islamic Revolution Guards Corps (IRGC) and Basiji (volunteer) forces opened fire to the authority and people from behind the stand during the parade," Governor of Khuzestan Gholam-Reza Shariati said, according to IRNA.
IRGC spokesman Ramezan Sharif said the attackers were affiliated with a terrorist group supported by Saudi Arabia, Press TV said. "The individuals who fired at the people and the armed forces during the parade are connected to the al-Ahvaziya group which is fed by Saudi Arabia," Sharif said. Saudi Arabia has yet to respond to the allegations.
The parade was part of nationwide celebrations in Iran to mark the 30th anniversary since the end of the eight-year war with Iraq that started in September 1980 and ended in August 1988.
The attack happened in a province bordering Iraq that has a large ethnic Arab community, many of them Sunni. It was a major battleground during the war that killed half a million soldiers.
Iranian Foreign Minister Mohammad Javad Zarif also blamed "a foreign regime" backed by the United States for Saturday's attack that killed at least eight troops and several civilians.
Terrorists recruited, trained, armed & paid by a foreign regime have attacked Ahvaz. Children and journos among casualties. Iran holds regional terror sponsors and their US masters accountable for such attacks. Iran will respond swiftly and decisively in defense of Iranian lives. pic.twitter.com/WG1J1wgVD9— Javad Zarif (@JZarif) September 22, 2018
"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."
Earlier, Iran's President Hassan Rouhani used the occasion of the military parades to compare US President Donald Trump to the former Iraqi dictator Saddam Hussein, Press TV reported.
Speaking at a military rally in Tehran, he said Trump will fail in the "economic and psychological war" he's launched against Iran, just as Hussein failed in his 8-year war against the Islamic Republic.
"Iran will neither abandon its defensive weapons nor will reduce its defense capabilities," Rouhani said.
"Rather it will increase its defense power day by day. The fact that they are angry at our missiles shows that these are the most influential weapons Iran has."
The Iraqi border crossing authority said Saturday that the Iranian side was temporarily closing al-Sheeb and al-Shalamcha border crossings between the two countries after the attack.