Islam's image has been tarnished by the violence of extremist groups such as Isis, Iranian President Hassan Rouhani said.

"It is our greatest duty today to correct the image of Islam in world public opinion," President Rouhani said during a conference on Islamic unity, in Tehran. "We must remove Islam's negative image from today's cyber and real space."

Most "violence, terror and massacres, unfortunately, take place in the Islamic world," he said.

"Did we ever think that, instead of enemies, an albeit small group from within the Islamic world using the language of Islam, would present it as the religion of killing, violence, whips, extortion and injustice?"

He said "financial and cultural poverty" are the main reasons Isis can recruit fighters.

He also criticised Muslim countries for "being silent in the face of all the killing and bloodshed" in Syria, Iraq and Yemen - all conflicts in which Iran plays a role.

The Islamic Republic supports Syrian President Bashar al-Assad, has close ties with neighbouring Iraq and condemns Isis. It is also an ally of the Houthi movement which seized control of most of Yemen last year.