The EU said al-Quds, an elite unit of the Islamic Revolutionary Guards Corps, "provided technical assistance, equipment and support to the Syrian security services to repress civilian protest movements," The New York Times reported.
There was no immediate reaction from the Syrian or Iranian governments about the sanctions, the first to single out Iran in the Syrian uprising against President Bashar Assad.
Activists in Damascus, Syria, hailed the move.
"The sanctions are great and very needed," said an opposition figure speaking to the Times anonymously out of fear of reprisal. "But I don't know how much they will help us on the ground to get rid of this regime. It is going to be a long battle."
The European Union has sanctions in place against 50 people and nine entities in the Syrian crackdown. The new measures freeze assets of people on the list and bar them from getting visas to travel in EU countries.
People sanctioned by the EU include five Syrian generals; Hassan Turkmani, a former defense minister and special envoy; Munir Adnuf, a Syrian army deputy; Samir Hassan, a businessman accused of being a government financier; and Maher Assad, the president's younger brother who leads the army's Fourth Division and is alleged to be responsible for much of the bloodshed.
The United States and other countries also accused Iran of aiding Assad's crackdown against protesters.
British newspapers recently quoted Western diplomats as saying Iran was providing riot control and surveillance equipment to the Assad government.