Boko Haram fighters are reported to have killed hundreds of people in a renewed assault after capturing a key town and military base in northeast Nigeria at the weekend, local officials have said.

The group's fighters initially captured the town of Baga and the headquarters of the Multinational Joint Task Force (MNJTF), which is made of troops from Nigeria, Niger and Chad, on Saturday.

At least 100 people were killed when the Boko Haram first took over the town on the edge of Lake Chad, the district head Abba Hassan said on Thursday. The fighters then razed several towns and villages in Borno state in the following days. 

Musa Bukar, head of the Kukawa local government area, said: "They [Boko Haram] burnt to the ground all the 16 towns and villages, including Baga, Doron-Baga, Mile 4, Mile 3, Kauyen Kuros and Bunduram."

Abubakar Gamandi, head of Borno's fish traders union and a Baga native, also confirmed the attacks, adding that hundreds of people who fled were trapped on islands on Lake Chad.

The armed group has seized more than two dozen towns in northeast Nigeria in the last six months, and now controls all three of Borno's borders with Niger, Chad and Cameroon.

The fighters reportedly used petrol bombs and explosives to destroy Baga, a key fishing and commercial hub, and the surrounding villages on the shores of Lake Chad.

Al Jazeera's Ahmed Idriss, reporting from Kaduna, said: "Effectively, Baga town is under Boko Haram control at the moment."

Idriss said that there were reports that hundreds of people had been killed in the violence and that some of those who fled are believed to have drowned in their attempt to escape to Chad and other neighbouring countries.

Deteriorating situation

Chad's Prime Minister Kalzeubet Pahimi has appealed for international aid for the thousands of Nigerian refugees who have fled the Boko Haram attacks

He said on Thursday that about 2,000 Nigerians and 500 Chadians crossed the border into Chad in recent days, joining around 1,000 Nigerians who arrived some months ago.

The UNHCR said: "Following insurgent attacks on five villages along the frontier between Chad and Nigeria between December 28 and December 30, the humanitarian situation has deteriorated."

The UN refugee agency put the total figure of Nigerian refugees in Chad at more than 5,000.

Gamandi said that a head count would have to be conducted to determine the number of dead and missing but that could pose difficulties as residents fled both towards Maiduguri and also into Chad.

About 560 villagers have been stranded on an island on Lake Chad since Saturday without food, he added.

"They told me that some of them are dying from lack of food, cold and malaria on the mosquito-infested island," he said.

Army concerns

Nigeria's military, West Africa's largest, has come under scrutiny for its inability to fight Boko Haram after reports of a lack of adequate weaponry and even bullets.

Boko Haram, in contrast, has been seen with advanced weapons, including rocket-propelled grenades, heavy machine guns and even a tank.

The armed group has waged a fight to establish Islamic law in the country's northeast for five years.

The number and scale of attacks rose sharply last year, after the government imposed emergency rule on the three worst-hit states. 

Boko Haram has also launched cross-border attacks into Chad and Cameroon.

Source: Al Jazeera