A group of gunmen raided a prison outside Nigeria’s capital city of Abuja on Monday, killing two guards and freeing about 30 prisoners.

Federal police spokesman Frank Mba said two suspects in the attack have been arrested and 25 of the escaped prisoners have been recaptured, according to the Associated Press.

No group has claimed responsibility for the incident, but analysts suspect Boko Haram, a militant insurgent group that seeks to impose Islamic law, or Shariah, in the country.

Monday’s early-morning ambush occurred at the Special Anti-Robbery Squad, or SARS, headquarters just outside the capital. The facility houses detainees who are being transferred to prisons in the capital, as well as many suspected Boko Haram militants.

The SARS facility was criticized by an Amnesty International report this month. The human rights watchdog found that many prisoners there are denied their basic legal rights, and sometimes subjected to beatings, lack of food and water, and other inhumane conditions.

Authorities said no terrorism suspects escaped following Monday’s attack.

The prison ambush followed on the heels of another bloody incident. On Sunday, suicide bombers killed at least 11 people at Nigeria's Armed Forces Command and Staff College in Jaji, a city north of Abuja.

Boko Haram – which means "Western education is sacrilege" – was founded in 2002 but has become increasingly militant in recent years, killing more than 1,000 people since the group’s founder and spiritual leader, Mohammed Yusuf, was killed in a 2009 government offensive.

In recent months, the group has been targeted by national security forces in a series of raids. But incidents like Monday’s prison attack are still frequent, making clear that Boko Haram members and other militants are still quite active in Africa’s most populous country.

The ongoing insurgency has strained the fragile relationship between Nigeria’s mostly Muslim northern regions and its predominantly Christian south. The south is generally more developed than the north, where poverty and unemployment make it easier for Boko Haram and affiliated groups to recruit new members.

Officials sources are playing down the possibility that Boko Hara instigated Monday’s prison raid, especially since SARS is well-guarded, a high-security facility located next to several government buildings.