- Boko Haram has terrorized northern Nigeria regularly since 2009
- The Islamist group aims to impose a stricter enforcement of Sharia law
"Boko Haram overwhelmed the Multinational Joint Task Force and dislodged them from their base outside Baga after hours-long fighting," said Maina Ma'aji Lawan, a Nigerian senator from the state of Borno, where Baga is located.
"They came in huge numbers heavily armed and subdued the multinational troops consisting (of) soldiers from Nigeria, Niger and Chad," Lawan said.
The Multinational Joint Task Force (MNJTF) was formed in 1998 to combat light arms proliferation and human trafficking. More recently, it has been involved in the fight against Boko Haram.
It was not immediately clear how many troops were at the base at the time of the attack, which happened Saturday.
Baga resident Yusuf Maidaji fled to the Chadian village of Kangallam.
He said the militants in Baga torched hundreds of homes and looted shops. He also said people were killed, but that it was difficult to know how many.
"The toll could be huge because the gunmen opened indiscriminate fire on fleeing residents," said Maidaji.
has terrorized northern Nigeria regularly since 2009, attacking police, schools, churches and civilians, and bombing government buildings.
The Islamist group -- considered one of the world's most deadly terrorist organizations -- has said its aim is to impose a stricter enforcement of Sharia law across Nigeria, which is split between a majority Muslim north and a mostly Christian south.