BENGHAZI, Libya (Reuters) - Seven Iranian relief workers who had been taken hostage by an armed group in July in the Libyan city of Benghazi were freed on Saturday, a Libyan security source and the Libyan Red Crescent Association said.

The seven Iranian men arrived in Benghazi in late July as guests of the Libyan Red Crescent to help with relief work in the city. They were seized from their vehicle by an unknown armed group in the heart of Benghazi.

Mohamed El-Misrati, spokesman for the Libyan Red Crescent, told Reuters: "With the cooperation of the local council in Benghazi, the seven relief workers were released. They are in good health and en route to Iran."

The security source said they were released about midday. It was not immediately clear who freed them, or why now.

Their abduction is one of several violent incidents that have rocked the birthplace of last year's revolt that toppled veteran ruler Muammar Gaddafi.

Libya's new rulers have struggled to impose their authority on a country awash with weapons, and many Libyans are fed up with militias that formed during the war but which still patrol the streets and often take the law into their own hands.

Thousands of Libyans marched in Benghazi in September in support of democracy and against the Islamist militias that Washington blames for an attack on the U.S. consulate there that killed four Americans including the ambassador earlier in the month. (Reporting by Omar al-Mosmary in Benghazi; Writing by Shaimaa Fayed in Cairo; Editing by Alison Williams)