Nigerian President Muhammadu Buhari has replaced four of the country's top military heads following months of pressure over the nation's worsening security crisis. 

Buhari, who took office in 2015 with a pledge to stamp out the Boko Haram Islamist insurgency, had long ignored advice to dismiss the commanders of Nigeria's army, navy and air force, as well as the chief of defense staff. He announced their resignation and replacements on Twitter on Tuesday.

A recent spate of skirmishes in south-eastern Nigeria between the army and the separatist Indigenous People of Biafra group (IPOB) has further deepened Nigeria's security woes. 

Coupled with Boko Haram's continued presence in the north and a spike in armed banditry, swathes of Nigeria remain near-ungovernable.

"Nigeria is probably more insecure than it's been in recent history," Ryan Cummings, the director of analysis for the Africa-focused risk management consultancy Signal Risk, told DW.

New chiefs face 'high expectations'

The reshuffle saw Major General Lucky Eluonye Onyenuchea Irabor become Chief of Defense Staff and Ibrahim Attahiru become Chief of the Army. The air force and navy now have new leaders in Air Vice-Marshal Isiaka Oladayo Amao and Rear Admiral A.Z. Gambo, respectively.

Presidential spokesman Malam Garba Shehu said the reshuffle was "routine" and endorsed the new leaders.

"None have them have served less than 30 years in the armed forces," he told DW. "I think they are well-equipped to carry out the task at hand as long as the government gives them support."

Kole Shettima from the Center for Democracy and Development told DW the new chiefs will be facing "high expectations, especially given that three of the four were at one point deployed to the north-east."

Shettima believes coordination and personal understanding between the new leaders would be a big factor in their potential success.

"I think everyone probably knew the previous service chiefs were not even on talking terms and that undermined their ability to prosecute the war against the insurgency," he says. 

For Cummings, the reshuffle is a sign of Buhari's "exasperation and toughness."

"The buck has been passed on to the four figures that have been removed from their respective offices rather than the president himself," he says.

Cummings adds that many of Nigeria's security threats are "rooted in systemic issues," such as resource challenges.

"This is not an issue where a simple change in military leadership all of a sudden addresses both symptoms and causes of insecurity in the country," he explains.

Fighting ongoing in southern Nigeria

Developments in south-eastern Nigeria have taken a violent turn this week, with clashes between members of IPOB's newly formed armed wing, the Eastern Security Network, and the Nigerian military.

There are reports of deaths on both sides. The origin of the flare-up is disputed, but correspondents say the Nigerian army retaliated after IPOB members allegedly killed soldiers.

In the town of Orlu near the Imo state capital Owerri, eyewitnesses said there was sporadic shooting, with residents taking cover to avoid stray bullets. The Imo state government has since imposed a dusk-to-dawn curfew in affected areas.

Resident Nawwal Yusuf placed the blame on IPOB "agitators."

"They attacked the northerners and killed four of them," he told DW. "We discovered four dead bodies. They have already been buried."

Peter Uche, a member of IPOB, told DW the separatist group had been repeatedly harassed by the government since starting a security outfit in their region.

"The soldiers and this government have been kicking against the IPOB members," he said. "I am not happy about it. Other regions in this country have their own security outfit. But we have been fighting, they have been fighting us, trying to eliminate us."

Separatist movement remains active

Historically, south-eastern Nigeria has been a hotbed for Biafran separatist agitation.

The Nigerian Civil War, which lasted from 1967 to 1970, pitted southern separatists — who wanted to form the independent nation of Biafra — against the Nigerian government.

There are also religious divisions between predominantly Muslim northerners and southerners, who are largely Christian.

Currently, numerous splinter groups in south-eastern Nigeria are loosely united, demanding the right to form their own state. IPOB's leader, Nnamdi Kanu, is in exile. 

The region is one of Nigeria's richest in terms of mineral resources, specifically oil. But with oil prices currently low, the Nigerian government is struggling to finance its budget.

"You have a population and Igbo population that feels somewhat disconnected from Nigeria's federal government structures," says Cummings. "They feel that President Buhari does not specifically represent their interests."

But despite the increasingly loud calls from the IPOB for the formation of the state of Biafra, Cummings adds that, despite dissatisfaction with the Nigerian government, wider polls show there is "not much resonance" for separatism in the region.