Officers fired tear gas to disperse crowds in several north-western cities and towns, and there were many arrests.

The protests were sparked by a children's television programme aired on Friday that ridiculed the accents of Azeris and included offensive jokes.

The state broadcaster has apologised for the "unforgivable mistake".

"The managers and individuals involved in this regrettable issue which offended our Azeri-speaking compatriots will be seriously confronted and this incident will be fully investigated," the head of Islamic Republic of Iran Broadcasting (IRIB), Mohammad Sarafraz, was quoted as saying by the Fars news agency.

"We will increase our efforts to strengthen ethnic unity and national cohesion."

There are approximately 13 million ethnic Azeris in Iran, or 16% of the population.

The US state department says Azeris are well integrated into government and society, but that they have accused the government of discriminating against them by prohibiting the Azeri language in schools, harassing Azeri activists or organisers, and changing Azeri geographic names.

Azeri groups also say a number of Azeri political prisoners have been jailed for advocating cultural and language rights for Azeris. The government has charged several of them with "revolting against the Islamic state".