Kano - Nigerian fighter jets have bombed the northeast town of Malam Fatori, controlled by Boko Haram, the military said Thursday.
Witnesses and some media reports said troops and airforce planes from neighbouring Chad were involved in the operation on Nigerian soil but Abuja neither confirmed nor denied the claim.
There was no initial word on casualties or whether Boko Haram fighters had fled the area.
"Malam Fatori is within the area of operation covered by the Multinational Joint Task Force (MNJTF) of which Chad has always been a part," defence spokesman Chris Olukolade told AFP in a text message.
"The Nigerian airforce has also been conducting (an) air mission there for two days now," he added. "It is all part of the ongoing efforts against terrorism."
The MNJTF was set up more than a decade ago to combat smuggling in the remote region but as the Nigerian Islamist insurgency in the area intensified, the mandate of the force changed.
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Residents in the town of Bosso, which lies next to Malam Fatori but across the border in Niger, said the bombardment began early on Wednesday and lasted for several hours.
"At around 8:00 am (0700 GMT) we started seeing three military jets encircling Malam Fatori and soon after (they) began dropping bombs," said Idrissa Ari, a Bosso resident.
Reaching locals inside Malam Fatori is difficult given the collapse of the mobile phone network on the Nigerian side of the border.
The authorities in N'Djamena did not respond to requests seeking comment on their alleged involvement in the operation.
The Boko Haram uprising has become a regional crisis, with the four directly affected countries, Cameroon, Chad, Niger and Nigeria -- agreeing to boost cooperation to contain the threat.
The African Union's annual summit in the Ethiopian capital Addis Ababa is this week expected to focus heavily on the threat from Boko Haram.
AU chief Nkosazana Dlamini-Zuma has called the insurgency "a threat to the whole continent".Chadian troops in Cameroon
A brutal attack this month on the Nigerian town of Baga, near Chad and Niger, killed several hundred people and raised fresh questions about the Nigerian military's capacity to face Boko Haram alone.
An aerial bombardment inside Nigeria by the Chadian airforce, if confirmed, would mark a major development in bilateral security cooperation.
While it was unclear whether Chadian troops had begun operating in Nigeria, security sources said soldiers from Chad had arrived in Cameroon ahead of an expected campaign against the Islamists.
"The first Chadian soldiers were deployed yesterday (Wednesday) in Fotokol," a Cameroonian security source told AFP, requesting anonymity.
Fotokol is just 500 meters (0.3 miles) from the Nigerian town of Gamboru, currently controlled by Boko Haram.
A senior Cameroonian officer said the deployment was part of "preliminary action" for the Chadian army to take on Boko Haram alongside troops from Yaounde.
The insurgents control large parts of Nigeria's Borno state, which shares borders with Cameroon, Chad and Niger.
Meanwhile, local sources in three areas of Cameroon's far north reported that 10 people had their throats slit by suspected Boko Haram militants this week.