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Unknown gunmen have attacked a Nigerian police base in the capital, Abuja, where Boko Haram Islamist militants are often held, police say.
A police spokesman said the attack was repelled. Unconfirmed reports say some detainees were freed.
The Special Anti-Robbery Squad (Sars) headquarters is near several government buildings and security is normally extremely tight in the area.
No group has said it carried out this attack but Boko Haram is suspected.
The group wants to establish Islamic law in Nigeria and has killed hundreds of people this year, mostly in the mainly Muslim north.
The attack comes a day after a double suicide bombing killed 11 people in a church inside a military barracks in Kaduna state, north of the capital.
One Abuja resident said he heard gunfire for about half an hour in the early hours of Monday morning.
A police spokesman did not give any further details.
An AFP journalist at the Sars headquarters says there are no visible signs of damage to the building, which is heavily guarded with two armoured vehicles outside.
Armed robbery suspects are also often detained at the building.
It is where suspects are held when they are first transferred to the capital.
While most Boko Haram attacks are carried out in the north, it has previously targeted Abuja.
Last year, a suicide bomber from the group attacked the main police headquarters in the capital killing six people.
The militants have also previously attacked prisons and freed hundreds of suspected Boko Haram members.