Iran's Basij militia, which played a key role in crushing opposition protests in 2009, has put on a show of strength in the capital in a two-day exercise culminating Thursday.
Some 50,000 members of the largely volunteer force were taking part in the drill, which was intended to "prove the security forces' ability to safeguard national security," Basij spokesman General Nasser Shabani told Iranian media.
Shabani recalled the role played by the militia in 2009, when defeated reformist candidates led mass street protests against the controversial re-election of hardline president Mahmoud Ahmadinejad.
"Considering our experience of events in 2009 as well as our past experiences, we planned this drill to demonstrate the security" aimed for by Iran's supreme leader Ayatollah Ali Khamenei, he said.
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Ahmadinejad's moderate successor, President Hassan Rouhani, has overseen a limited opening to the West that culminated in a long-elusive nuclear deal with world powers in July.
But the defeated reformist candidates of 2009, Mir Hossein Mousavi and Mehdi Karroubi, remain under house arrest and are derided by state media as the "heads of sedition."
Established by Iran's revolutionary leader Ayatollah Ruhollah Khomeini, the several hundred thousand strong Basij has always seen its primary role as defending the values of the revolution.
A senior commander, General Hossein Salami, hailed the force as the "eternal shield" protecting "the sacred system of the Islamic republic."
Largely recruited from among poorer Iranians, the Basij also plays an important social role, being deployed in vaccination campaigns and relief efforts after earthquakes and other natural disasters.