Buhari, who ruled Nigeria from a coup in December 1983 to his ouster in 1985, told a seminar in Kaduna, northern Nigeria, at the weekend that the strict Islamic law code known as the Sharia should be introduced in full across Nigeria.
"I will continue to show openly and inside me the total commitment to the Sharia movement that is sweeping all over Nigeria," Buhari said, quoted in press reports.
"God willing, we will not stop the agitation for the total implementation of the Sharia in the country," Buhari said.
Northern Nigeria is mainly Muslim but southern Nigeria is mainly Christian and has led criticism of the introduction of Islamic law in a dozen northern states in the past 18 months.
Africa's most populous country has been shaken repeatedly in the past by religious unrest. In February 2000 between 2 000 and 3 000 people were killed by Christian-Muslim riots in Kaduna over the introduction of Sharia.
Call for Sharia across the country
Buhari's comments were interpreted by the southern-based papers as a call for the imposition of Sharia all across the country, even in the mainly Christian south.
"Buhari calls for Sharia in all states," was the headline of the respected newspaper The Guardian.
Buhari's comments were defended by supporters as simply a call for the full implementation of Sharia in areas where Muslims predominated.
But the comments are the second by Buhari that have courted controversy after he called earlier this year for Muslims to vote at the next presidential elections only for someone who would defend their faith.
This was criticised by the press as a call for voting along religious lines, as well as an attack on the current president, Olusegun Obasanjo, who is a Christian.
Buhari made the latest comments at a seminar organised by the Supreme Council for Sharia in Nigeria, a newly set up body attended by northern state governments and Islamic scholars.
"It is a legal responsibility which God has given us, within the context of one Nigeria, to continue to uphold the practice of Sharia wholeheartedly ... and to educate non-Muslims that they have nothing to fear," he said.
"What remains for Muslims in Nigeria is for them to redouble their efforts, educate Muslims on the need to promote the full implementation of Sharia law," he went on. - AFP