Suspected Boko Haram militants have killed several people in two attacks on Nigerian villages that occurred after the government announced a ceasefire to enable 200 abducted girls to be freed, security sources and witnesses said on Saturday.
However, the government cast doubt on whether the attacks really were Boko Haram or one of several criminal groups that are exploiting the chaos of the insurgency. A spokesman said talks to free the girls would continue in Chad on Monday.
The fresh attacks dashed hopes for an easing of the northeast's violence, although officials remained confident they can negotiate the release of girls whose abduction by the rebels in the remote northeastern town of Chibok in April caused international shock and outrage.
A presidency and another government source said they were aiming to do this by Tuesday.
Boko Haram, whose name translates roughly as "Western education is sinful," has massacred thousands in a struggle to carve an Islamic state out of religiously mixed Nigeria, whose southern half is mainly Christian in faith.
Nigeria's armed forces chief Air Chief Marshal Alex Badeh announced the ceasefire on Friday. On Saturday, two senior government sources said it aims to secure the girls' release as early as Monday or Tuesday, although they declined to give further details.
In the first attack, suspected insurgents attacked the village of Abadam on Friday night, killing at least one person and ransacking homes, while another assault on the village of Dzur on Saturday morning left at least eight people dead.
"I was just boarding a bus when the gunshots started," Adams Mishelia, who was in the adjacent town of Shaffa, said of the Dzur attack. "People were fleeing into the bush, so I got off the bus and headed to the bush too. I later learned they slaughtered eight people."
A security source confirmed that attack and the assault on Abadam the night before. Mohammed Bulama, a resident of the main northeastern city of Maiduguri, told Reuters he lost his uncle in the Abadam attack. Other casualties there were unclear.
"DISCUSSIONS IN CHAD"
When asked about the violence, government spokesman Mike Omeri said by telephone that "the BokoHaram people have also said that some attacks are not undertaken by them."
Boko Haram, seen as the biggest threat to Africa's top economy and oil producer, is believed to be divided into several factions that loosely cooperate with each other, and it is unclear with which faction the government has been negotiating.
"Discussions will continue in Chad next week, and on the basis of those discussions we'll have more details," on how the girls will be released, Omeri said.
The announcement of the truce came a day before a rally of supporters of President Goodluck Jonathan inAbuja attended by his vice president, Namadi Sambo, although an expected announcement of Jonathan's candidacy for February 2015 elections did not materialize during the rally.
Officials at the presidency and military did not immediately respond to requests for comment.
Boko Haram has also not yet commented on the reported truce. The group's sole means of conveying messages is via videotaped speeches by a man claiming to be Abubakar Shekau, its leader whom the military last year said it had killed.
A history of abortive government attempts at truce deals with Boko Haram and military claims to have rescued some girls that proved false, mean Nigerians are likely to greet the newly reported breakthrough with skepticism.
The second government source said: "We are negotiating with considerable caution. Boko Haram has grown into such an amorphous entity that any splinter group could come up disowning the deal. (But) we believe we are talking to the right people."
The talks were held with a formerly unknown militant called Danladi Ahmadu, who says he is the group's "secretary general."
Underlining the uncertainty over the chain of command in Boko Haram, Nigeria's military said at the end of last month a man who had been posing as Shekau in the group's growing number of videos had been killed in clashes over the town of Konduga.
The schoolgirls' abduction stunned the world, spurred a global Twitter campaign to get them rescued and heaped pressure on Jonathan's administration to do more to protect civilians in the northeast where BokoHaram's insurgency is focused.
Several rounds of negotiations with the jihadist movement have been pursued in recent years but they have never yielded calm, partly because of Boko Haram's internal divisions.
Since the girls' kidnapping, the Nigerian military has twice asserted that it rescued some or all of the girls, only to have to backtrack hours later.
At Saturday's rally in Abuja, many of President Jonathan's supporters wrapped themselves in the white and green of Nigeria's flag and sang and danced under a banner reading "We Love You Goodluck Jonathan. Our support is 100 percent."
Two candidates for the main opposition coalition, former military ruler Muhammadu Buhari and ex-vice president Atiku Abubakar, have declared their candidacy against Jonathan.