Iran's semi-official ISNA news agency says a closed trial has begun for 21 suspects in the storming of Saudi diplomatic missions earlier this year.
Monday's report did not provide further details.
Protesters stormed the Saudi Embassy in Tehran and a consulate in Mashhad in January after Sunni-ruled Saudi Arabia executed Sheikh Nimr al-Nimr, a prominent Shiite cleric and dissident. Iran views itself as the defender of the world's Shiites.
The attacks on the diplomatic missions led to the severing of diplomatic ties between Saudi Arabia and Iran, regional rivals who back opposite sides in the wars in Syria and Yemen.
In April, Iran said 48 people, including four clerics, would be tried in relation to the storming of the diplomatic missions.