Boko Haram sacked two military bases in northeast Nigeria as the jihadist fighters battle for control of a strategic town on Lake Chad, military sources said on Thursday.

Islamic State West Africa Province fighters overran a naval base and a Multinational Joint Task Force (MNJTF) post in the fishing town of Baga after a fierce battle overnight on Wednesday, December 26, the sources told AFP.

Fighters in several vehicles stormed Baga and engaged troops in intense fighting at the MNJTF base which hosts units from Nigeria, Niger, Chad and Cameroon.

The insurgents also sacked a naval base in Mile 3 which lies 3 miles (5 km) from Baga, a military source who asked not to be identified told AFP.

“The troops were overpowered and forced to withdraw,” the source, adding that “the terrorists carted away guntrucks, ammunition and multiple rocket launchers from the base.”

Troops from the two bases withdrew to another naval base at Fish Dam on the shores of Lake Chad, the military source said.

That base was well secured, and resisted several attempts by Boko Haram fighters to overrun it, the source added.

The jihadists then retreated and the troops decided not to pursue them to avoid running into an ambush, a strategy Boko Haram often employs against the military, the officer said.

Nigerian army spokesperson Sani Usman confirmed the attack in a Facebook post which said the assault began at about 7 p.m. local time (1800 GMT).

“The troops along with their Nigerian Navy counterparts put up a very determined fight” all night, he said, adding that one navy member was killed.

Troop reinforcements were in pursuit of the Boko Haram fighters and the Nigerian Air Force was also mobilised and engaged the fleeing fighters, he said.

Residents of the regional capital Maiduguri reported seeing six fighter jets flying towards Baga on Thursday.

People arriving from Baga are saying ISWAP assured civilians they & their property safe, they just wanted the equipment in MNJTF barracks. Apparently it's been burnt, including the naval base where SBS special forces were holding out. — Obi Anyadike (@Enugu62) December 28, 2018

In January 2015, Boko Haram overran the MNJTF base and took control of Baga, killing hundreds of residents and forcing thousands to flee to Maiduguri. The town was later retaken, but jihadists continue to attack the military and civilians in the area, which is an ISWAP stronghold.

Its fighters occupy camps on many islands in Lake Chad.

Update December 29 ISIS claimed ISWAP fighters were responsible for the Baga attacks, saying that dozens of military personnel were killed and injured and four were captured. It said “several” barracks were burned.

The photoset also showed #ISWA seize plenty of weapons, equipment and vehicles from the military base at #Baga pic.twitter.com/f4eluzak7C — Robert Postings (@RobertPostings) December 29, 2018

Update December 31 On Sunday, ISIS released a video of the attack of Fish Dam and the Nigerian Air Force released a video of strikes in the area.

Boko Haram has repeatedly struck military outposts in the region in recent months, and the Lake Chad area around Baga has seen a number of attacks attributed to ISWAP in recent weeks.

On December 17, Boko Haram militants killed one soldier and injured another when they briefly seized a military base in Mairari village close to the garrison town of Monguno, around 52 km (32 miles) from Baga.

On December 14, ISWAP fighters attacked a military base in Gudumbali, around 70 km (44 miles) from Baga. The Nigerian army said one solder was killed, and ISIS claimed ISWAP fighters killed five troops, while other reports said a dozen or more died. Ten days earlier, ISWAP fighters launched an assault on a military base in Gudumbali, sparking a fierce firefight in which two soldiers were injured.

ISWAP fighters attacked a military base in Mallam Fatori, around 82 km (51 miles) from Baga on December 3. At least one soldier was killed and several others were injured in the attack.

Also on December 1, ISIS claimed ISWAP killed eight Nigerian soldiers and wounded 17 others in an attack near Gamboru, around 90 km (56 miles) from Baga. The Nigerian Army said that it captured weapons and stores during “offensive patrols” in the area, but did not mention army casualties. On December 14, the Shekau faction of Boko Haram was blamed when Nigerian soldiers were killed in roadside bomb blast near Gamboru.

On November 30, ISWAP fighters attacked a military base in Arege village near Baga, killing at least on soldier and injuring at least seven others. The same base came under attack two days earlier, but the militants failed to overrun it.

Two days earlier, three soldiers were killed in attack on a military base in Cross-Kauwa, around 24 km (15 miles) from Baga.

Surge in Boko Haram attacks

Boko Haram split into two factions in mid-2016 over ideological differences. One is led by Abu Mus’ab Al-Barnawi and largely focuses on attacking military and government targets, while the other, led by Abubakar Shekau, is notorious for suicide bombings and indiscriminate killings of civilians.

Shekau has pledged allegiance to ISIS leader Abu Bakr Al-Baghdadi, but ISIS central gave its formal backing to the Barnawi faction, which is known as Islamic State West Africa Province.

ISWAP has lately intensified its armed campaign, launching a number of major assaults on military targets in Borno and neighboring Yobe state amid signs of a takeover by more hardline leaders.

There have been dozens of attacks on military bases since July. Most of the attacks have been blamed on ISWAP, or claimed by ISIS as ISWAP attacks, but there has been an upsurge in attacks by both factions in recent weeks.

In the most recent major attack on December 24, Boko Haram militants ambushed a military convoy between Maiduguri and Damaturu, killing more than a dozen military and police personnel, the army said. But an officer, speaking on condition of anonymity, said the militants had overrun an army base, and put the death toll at 18.

That attack followed an attempted raid on a nearby military base in Kukareta village, 20 km (12 miles) from Damaturu.

The military on November 30 lashed out at the media, saying some media outlets were “creating erroneous impression of the Nigerian Army through inaccurate and false publication of casualty figures.”

The military has even threatened legal action against organizations publishing unofficial figures.

Borno and Yobe states, along with nearby Adamawa state, have born the brunt of nine years of jihadist violence that has claimed 27,000 lives and forced 1.8 million people to flee their homes. The conflict has also spilled over into Nigeria’s northern neighbours Chad, Niger and Cameroon.

The recent surge in Boko Haram attacks has increased pressure on President Muhammadu Buhari, who was elected in 2015 on a promise to defeat the Islamists and has repeatedly said they are virtually defeated. His administration wants to show it is winning the fight against Boko Haram ahead of a presidential election in February at which he will seek a second term in office.

With reporting from AFP