At least 20 people were killed in revenge attacks on Muslims in Nigeria yesterday as religious riots intensified a day after the country's leading Anglican archbishop warned Muslims that they did not have a "monopoly on violence".

Christian mobs with machetes and guns roamed the streets of the mainly Christian city of Onitsha, in the south-east, in retaliation for Muslim violence in the north earlier this week which killed dozens of people, destroyed churches and left thousands homeless.

Troops were powerless to resist the mobs. Revenge attacks were also reported in another south-eastern city, Enugu, where the Red Cross said at least seven people were killed and 150 injured. At least 73 people have been killed in the past five days.

The Christian retaliation came after a widely publicised statement by the powerful Anglican primate, Peter Akinola, who warned that community leaders may not be able to contain "restive youth".

"May we at this stage remind our Muslim brothers that they do not have the monopoly on violence in this nation," he said.

He said the Muslim riots, which broke out at the weekend in response to the cartoons of the prophet Muhammad that have generated fury across the Muslim world, were part of a plot to make Nigeria an Islamic country.

"It is no longer a hidden fact that a long-standing agenda to make this Nigeria an Islamic nation is being surreptitiously pursued," he said.

Mr Akinola is also known for his opposition to allowing gays to be priests in the Anglican church. He could not be reached for comment on the outbreak of the violence in Onitsha.

The violence erupted on Saturday in the northern city of Maiduguri. Thirty Christian churches were razed and 18 people were killed, mostly Christians. There was also violence on Monday and Tuesday in the northern city of Bauchi, where witnesses and Red Cross officials said 25 people were killed when Muslim mobs attacked Christians. Bauchi was tense but calm yesterday as police and soldiers patrolled the city. But the focus quickly turned to Onitsha where retaliation flared.

"There are thousands of boys with cutlasses and sticks on the rampage," said George Esiri, a Reuters photographer. "I've counted at least 20 bodies here by the Onitsha bridge."

He said the dead were Hausas. "Some of them are burnt and some have their stomachs cut open," he said.

Mr Akinola blamed "influential Muslims" for supporting the religious extremists behind the attacks.

Nigeria is roughly divided between the mainly Muslim north and the Christian south. Thousands of people have died in religious violence since 2000.