Nigeria's military has called for support in tackling Boko Haram after a major attack on a key northeast town that is feared could be the worst in the bloody six-year insurgency.

There are still no independently corroborated figures for the huge numbers said to have been killed in Baga, on the shores of Lake Chad in the far north of Borno State.

But defence spokesman Chris Olukolade said in a statement issued late Saturday that the description of the assault as "the deadliest" in a conflict that has claimed more than 13,000 lives since 2009 was "quite valid".

"The attack on the town by the bloodhounds and their activities since January 3rd, 2015, should convince well-meaning people all over the world that Boko Haram is the evil all must collaborate to end, rather than vilifying those working to check them," he said.

Nigeria's military -- west Africa's largest -- has faced repeated criticism for failing to end the six-year Islamist insurgency, as well as allegations of human rights abuses.

Soldiers have complained of a lack of adequate weapons and even refused to deploy to take on the better-armed rebels, who want to create a hardline Islamic state in northeast Nigeria.

With elections set for next month, Nigeria's government has also been accused of playing politics with the insurgency, as most of the areas worst affected by the violence are main opposition strongholds.

But Olukolade said: "The Nigerian military has not given up on Baga and other localities where terrorist activities are now prevalent.

"Appropriate plans, men and resources are presently being mobilised to address the situation," he said on defenceinfo.mil.ng, in the military's first detailed comment on last weekend's attack.

The military and government often makes such statements, without giving specific details, yet there are reports of attacks on an almost daily basis.

On Saturday, two explosions rocked northeast Nigeria, including one at a crowded market in the Borno State capital, Maiduguri, by a girl suicide bomber thought to be just 10. Nineteen people were killed.

The Baga attack, which local officials said forced at least 20,000 people to flee, also overran the headquarters of the Multinational Joint Task Force made up of troops from Nigeria, Niger and Chad.

Nigerien and Chadian soldiers were not at the base at the time.

Olukolade said 14 soldiers were killed and more than 30 injured as well as "several" insurgents.

There was no credible estimate yet of the numbers of civilians killed, after huge numbers cited locally, he added.

"It is necessary to reassure Nigerians that the Nigerian Armed Forces and security agencies are capable of flushing out the terrorists from Baga and all parts of the nation's territory where their activities are prevalent."

- Territorial gains -

Boko Haram has seized dozens of towns and villages in northeast Nigeria in the last six months and now reportedly controls the border areas of Borno state with Niger, Chad and Cameroon.

The territorial gains have led to fears of a total loss of government control in the remote region -- and a claim last year by a senior US diplomat that the military was in denial about the situation.

Olukolade maintained on Saturday: "No portion of Nigeria's territory has been or will be conceded to terrorists.

"The use of all available resources within the armed forces will continue to be maximised to sustain the tempo of the counter-terrorism campaign towards containing and eradicating terrorism in the nation's territory."