The leader of the opposition in Tunisia has been shot dead outside his home.

Chokri Belaid, leader of the Unified Democratic Nationalist Party, was shot four times by a gunman on a motorbike as he left his house in the capital Tunis.

Witnesses say he was taken to a nearby clinic and died.

Mr Belaid had been critical of Tunisia's leadership, especially the moderate Islamist party Ennahda that dominates the government, and violence by radical Muslims.

Government spokesman Samir Dilou called it an "odious crime".

The reason for the killing is unclear.

More than 1,000 Tunisians protested outside the Interior Ministry against the killing.

Tunisian police fired teargas to disperse protesters as an ambulance carrying Mr Belaid's body approached Tunis's main street.

Police also fired in the air and used teargas in Sidi Bouzid, the birthplace of the Arab Spring uprisings, to disperse demonstrators.

The killing comes as Tunisia struggles with social and religious tensions after its longtime dictator was overthrown in an uprising two years ago that set off revolts across the Arab world.