Many Nigerians see their police force as corrupt and brutal
Nigeria's police minister has launched a scathing attack on the force, accusing officers of killings, robbery and other abuses.
Ibrahim Lame said the lack of security was "condemnable and unacceptable".
Human rights groups have frequently accused Nigeria's police of abuses and corruption but it is rare for the government to make similar charges.
The national police chief blamed the security problems on poverty, corruption and religious tension.
Mr Lame told a meeting of police commanders: "The current rate of crime across the nation, rising cases of extra-judicial killings, human rights violations, robberies, high-profile assassination and deliberate failure to comply with government directives are testimony to the sheer incapacity or wilful defiance of police high command" to government directives.
Caroline Duffield, BBC News, Lagos
Nigeria's culture of police brutality - and impunity - is powerful and the history of investigations holding the authorities to account is poor.
The real problem is that police are trapped in a culture of corruption in which funds are stolen. Junior officers are expected to bribe senior officers - for promotion, for accommodation and for equipment.
They are sent to battle armed robbers without bullet-proof vests or enough ammunition. Both sides know such encounters are a fight to the death.
But the laws governing when officers are permitted to open fire are clear. And - it seems - they are often ignored.
Inspector General of Police Ogbonna Onovo said the police were "operating under unbearable conditions", reports the Vanguard newspaper, adding that criminals were often better armed than the police.
Last year, a BBC investigation found that staff in the mortuary in the south-eastern city of Enugu were unable to cope with the large number of bodies the police were delivering - many of whom had been accused of being armed robbers.
Amnesty International's Erwin van der Borght said: "The Nigerian police are responsible for hundreds of unlawful killings every year."
Mr Onovo also denied reports that armed robbers had ordered a bus driver to run over passengers on the Lagos-Benin highway last week - shocking pictures of this incident prompted the Senate to open an inquiry earlier this week.
He said a truck had killed the passengers who were on the road after their bus had been held up by the bandits.
The police face criticism for not even attending the incident.
But the BBC's Caroline Duffield in Lagos says Nigerians are accustomed to seeing bodies pile up.
A video aired on al-Jazeera television this year apparently showed police and soldiers shooting unarmed civilians in the head, after the siege of a religious sect.
Seventeen officers are under arrest.
Our correspondent says Nigeria's culture of police brutality - and impunity - is powerful and the history of investigations holding the authorities to account is poor