Nigerian President Muhammadu Buhari announced an investigation Monday into the procurement of weapons and equipment for the military over the past eight years, as part of a crackdown on corruption.

His spokesman Femi Adesina said in a statement national security adviser Babagana Monguno had launched a committee to "identify irregularities and make recommendations for streamlining the procurement process".

"The establishment of the investigative committee is in keeping with President Buhari's determination to stamp out corruption and irregularities in Nigeria's public service," Adesina said.

"It comes against the background of the myriad of challenges that the Nigerian armed forces have faced in the course of ongoing counter-insurgency operations in the northeast, including the apparent deficit in military platforms with its attendant negative effects of troops' morale."

Malpractice under past administrations had often resulted in the acquisition of "sub-standard and unserviceable equipment," he said.

Since taking office in May after being elected on an anti-corruption ticket, Buhari has dismissed his entire military top brass and sacked key officials of the country's giant NNPC oil firm in a bid to clamp down on graft.

His victory triggered a wave of optimism for oil-rich Nigeria, which has Africa's biggest population and economy but many deep and seemingly intractable problems.

Nigeria is fighting a six-year insurgency by Boko Haram jihadists in the northeast which has seen the deaths of more than 15,000 people and at least 1.5 million displaced.

The military has long argued that it is hampered by a lack of weaponry, and Buhari warned Washington last month that a US refusal to arm his troops because of "so-called human rights violations" was helping Boko Haram.

The US has vowed to help Nigeria defeat the insurgency but it is prohibited under law from sending weapons to countries that fail to tackle human rights abuses.

Buhari's office said on August 7 the government would step up domestic arms manufacture for the military to cut its reliance on foreign weaponry in its fight with the insurgency.

UN chief Ban Ki-moon, speaking in Abuja on Monday, hailed Nigeria's "greater stability and peace" under its new leader as he commemorated a deadly attack on the global body by Boko Haram militants in 2011 .

Boko Haram's brutality and in particular the mass kidnapping and enslavement of schoolgirls has shocked world opinion, but Nigeria's own security forces also face criticism.

In June, rights watchdog Amnesty International said there was sufficient evidence to launch an investigation into senior Nigerian officers for war crimes.