By Joe Bavier and Njuwa Maina
KADUNA, Nigeria (Reuters) - Relatives used a lull in the curfew in northern Nigeria on Wednesday to search morgues for their loved ones, after riots triggered by disputed election results killed at least 100 people in the mostly-Muslim region.
Former military ruler Muhammadu Buhari said the ruling People's Democratic Party (PDP) had conspired with the electoral commission to cook up results showing President Goodluck Jonathan won Saturday's presidential race.
"Those who rigged the elections are responsible for the spontaneous action of the people in some parts of the country," Buhari said of the violence, talking to foreign journalists at his residence in the capital Abuja.
Observers deemed the polls in Africa's most populous nation the most credible in decades and a clear break with a long history of votes marred by ballot-stuffing and fraud.
The government said the post-election violence, which has largely been brought under control by curfews and a heavy military presence, was "unprovoked and premeditated."
Those perceived to be supporters of the ruling party have been stabbed, hacked and shot to death by angry youths since Jonathan, a Christian southerner, defeated Buhari. Churches, mosques, homes and shops have been set ablaze.
Hundreds suffered gunshot and machete wounds, some of them children, in the worst of the violence on Monday and thousands were displaced. Morgues were overflowing.
"My brother went to work on Monday morning. He hasn't come back since," said Austin John, 23, who used a lull in a curfew to go from morgue to morgue searching in vain for his brother.
"I don't know what I will tell our mother."
Another morgue in Kaduna had 20 bodies in its cold chambers. The charred remains of at least another 20 lay on the floor.
Kaduna's deputy police chief Nwodibo Ekechukwu said hundreds of people had been arrested on charges including murder.
Buhari said manipulation of electoral commission computers had slashed his vote by up to 40 percent in the northern states of Kano and Katsina and that his supporters were chased away from polling stations in large parts of the south.
He said his party had proof of the allegations, that foreign observers had not monitored the vote closely enough in some areas, and that the manipulation had been enough to deprive him of what could have been a victory in the first round.
"INEC (the electoral commission) and the ruling party worked hand in hand," he said.
Africa's most populous nation is supposed to complete its cycle of elections with governorship votes in its 36 states on April 26, but diplomats question whether that will be possible in large parts of the north.
Homes belonging to ruling party members, INEC offices and police stations have been targeted, as have members of the National Youth Corps, who are helping run the elections.
"It's hard to see how INEC will be able to hold credible elections in states where there is an undeclared state of emergency, which is certainly the case in Kaduna," said one Western diplomat who has been observing the polls.
INEC said no decision had yet been made but that the security situation was under review.
There has also been unrest in smaller towns where there is less of a military presence. The burned out shells of trucks and cars lay along the 200 km (120 mile) stretch of road between Kano and Kaduna, a Reuters witness said.
Diplomats have criticized Buhari for failing to issue a clear call for calm to those rioting in his name. He has dissociated himself from the violence.
"I am bitter because it is so fraudulent. I am bitter because people have been taken for a ride," Buhari said.
"That is why there was unrest."
(Additional reporting by Joe Brock in Kano, Abdulwahab Muhammad in Bauchi; Writing by Nick Tattersall; Editing by Giles Elgood)