Gunmen shot dead two civilians and then used explosives to free 175 inmates from a prison in Nigeria's southern town of Akure overnight, a prison official said on Sunday.
Islamist sect Boko Haram and al Qaeda-linked group Ansaru have been behind several prison raids in recent years. It was not clear whether they were behind this jail break at Olokuta prison in Ondo state or whether they had members held there.
"The unknown gunmen numbering over 20 came at about midnight into the Olokuta prison through the main gate after using dynamite," Prison Comptroller Tunde Olayiwola told Reuters.
"The gunmen shot and killed two people while trying to get in ... Some of the escaped prisoners have been re-arrested," Olayiwola said, adding that some prison staff were injured in a gun battle and were receiving treatment.
Violence by Islamist groups is mostly confined to Nigeria's majority Muslim north but there have been attacks as far south as Kogi state, which borders Ondo.
Boko Haram, which wants to create an Islamic state in the north, has become the biggest threat to security in Africa's most populous nation and top oil exporter.
President Goodluck Jonathan has declared a state of emergency in the three worst affected states in the northeast and launched an intensified military push to end the insurgency.
Nigeria also suffers from widespread crime and corruption nationwide. In southern states such as Ondo, kidnapping and other violent crimes are common.