State television showed images of thousands of men and women marching on Friday through the city of Ahwaz in Khuzestan province, where days ago groups of Arab-Iranians attacked and set fire to cars and buildings and clashed with security forces.
Officials say the protests were sparked by circulation of a forged letter, supposedly written by a senior government official, which suggested ways to dilute Arab influence in southwest Iran - the heartland of the country's oil industry.
At least 3% of Iran's more than 70 million population is Arab, but in some parts of the southwest they are a majority.
Those taking part in the Grand Solidarity rally in Ahwaz on Friday carried banners and chanted slogans in Farsi and Arabic condemning the unrest and attacking the Islamic state's chief enemies.
"Oh Muslims, unite, unite!" they chanted. "Down with hypocrites, down with America, down with Israel!"
Many officials and politicians have accused Iran's foreign enemies and exile opposition groups of stirring up the recent unrest.
Authorities temporarily closed Aljazeera's Tehran bureau on Wednesday, saying its role in encouraging the violence was being investigated.
"The Iranian Arabs of Khuzestan have proven their devotion to Islam and are bound to safeguard the Islamic Republic"
Friday prayer leader
"The Iranian Arabs of Khuzestan have proven their devotion to Islam and are bound to safeguard the Islamic Republic," Ahwaz Friday prayer leader Mohsen Heydari told the crowd, the official Islamic Republic News Agency (Irna) said.
Ahwaz residents say a security clampdown has taken place since the unrest, with scores of Revolutionary Guards manning checkpoints and patrolling the streets.
Officials said on Wednesday that about 200 of those arrested had been freed but another 144 remained in detention.