The Human Rights Activists News Agency (HRANA) said it had documented at least 4,023 arrests between February 28, when the war started, and May 9.

Charges included espionage, threats to national security and communicating or sharing content related to the conflict with foreign media, it said.

"Iranian authorities have used the conflict to intensify national security narratives and justify arrests, restrictions on freedom of expression, and violence against civilians," it said.

Meanwhile, Iran's national police chief Ahmad Reza Radan had said Sunday that more than "6,500 traitors and spies" linked with the "enemy" had been arrested since anti-government protests peaked in January.

The authorities described the demonstrations as riots and put them down with a crackdown that left thousands dead, according to rights groups.

"The process of identifying and arresting elements associated with the enemy continues, and the police have not stopped their actions in the field of confronting rioters," Radan said, quoted by the IRNA news agency.

There has also been growing alarm over executions in Iran.

Rights groups have said that since the start of the war, Iran has executed 26 men seen as "political prisoners" -- 14 men charged over January protests, one more over 2022 demonstrations and 11 accused of links to banned opposition groups.

Six men have been hanged by Iran on charges of spying for Israel since the war began, according to reports in Iranian official media.

HRANA said it had also documented at least 3,636 fatalities, including 1,701 civilians, due to US-Israeli attacks on Iran in the war, which is currently on hold with an uneasy ceasefire.