Some residents who had fled Gamboru across the border into northern Cameroon went back to the frontier town last morning after hearing a rumour that Chadian and Cameroonian troops were providing security.
"We lost eight people to Boko Haram gunmen today (Friday)," said Babagana Bukar, a Nigerian from Gamboru now living in the town of Fotokol, just across the border in Cameroon.
"Some of our people went back to Gamboru after they were told the town was safe for them.... While they were inspecting their homes, Boko Haram gunmen on a motorcycle opened fire on them killing five men and three women," he said.
They managed to make it back across the bridge that forms the border and were being treated for their injuries, he added.
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Boko Haram fighters have been seen going in and out of Gamboru for months, sometimes firing rocket-propelled grenades towards Fotokol, according to those who fled.
The group, which has been pushed out of captured towns across Nigeria's northeast by a four-nation coalition since February, are said to be dispersed in remote parts of the hard-to-reach region.
More than 550 people have been killed, increasing pressure on Buhari to bring an end to the violence.
A new, strengthened regional force is due to deploy against Boko Haram by the end of this month.