By Martin Plaut
BBC News Africa analyst
Radical Islamists have attacked government buildings in two northern Nigerian states, a day after clashes erupted in a third state in the region.
The trouble centres on a radical Islamist group whose spiritual leader, Mohammed Yusuf, lives in Maiduguri, the capital of Borno State.
Tensions have been growing between Mr Yusuf's followers and authorities.
Police recently raided buildings used by the preacher's followers after being tipped off by local people.
They seized weapons and ammunition.
There are reports that Mr Yusuf threatened to attack the police after a number of his followers were killed during a funeral in June.
But the roots of this issue go back several years.
Despite 12 northern Nigerian, mainly Muslim, states adopting Sharia law following the end of military rule in 1999, radical Islamists like Mr Yusuf believe their governments are too influenced by Western liberal values.
He has attacked Western education, including the work of the university in Maiduguri, declaring it to be haram (forbidden).
His preaching attracted a number of university students, who left their studies to join his movement.
It is these students who have spread Mr Yusuf's message to neighbouring states.
But his views are not supported by many local Muslims - who have prevented him from using their mosques, and called in the authorities.
Ustaz Hussein Zaccariah, a Muslim scholar based in the Nigerian capital, Abuja, said that the group led by Mohammed Yusuf were ignorant about what the Islamic religion really is.
"Three prominent Muslim groups in Borno state have been criticising them, saying their approach is wrong, their conception is wrong and everything about them is un-Islamic," he told the BBC's Focus on Africa programme.
Moses Aregbode, the Assistant Inspector General of Police in charge of north-eastern Nigeria, said that the membership of the group, known locally as the Taliban, has grown, but that they can still be contained.
"The police represent a symbol of government's authority," he said.
"Perhaps they have the intention of ousting government, and that is why they are massing their forces."