Updated

Armed men attacked a prison in Congo's eastern city of Beni on Sunday, killing at least 11 and freeing more than 900 prisoners, a government official said.

Eight prison guards were among the 11 dead, said North Kivu provincial governor Julien Paluku. About 30 prisoners remained in the Kangbayi prison following the afternoon attack, he said.

Paluku announced a curfew in Beni and nearby Butembo.

"Only the army and the police have the right to circulate in order to have control over the enemy," he said.

It was not immediately known who carried out the attack, although Allied Democratic Forces rebels are imprisoned there and the group has threatened attacks to free its members.

The ADF rebel group was founded in neighboring Uganda in the 1990s and is now based in Congo where it has intensified its attacks. The rebel group has killed more than 1,000 people in eastern Congo since October 2014.

A Congolese court in March sentenced to death nine ADF rebels prosecuted for crimes against humanity, terrorism and participation in a rebellion as part of increased efforts to hold the group accountable for attacks in Beni and surrounding towns and villages.

Scores of armed groups fight for control in Congo's mineral-rich eastern region.

Sunday's attack follows others carried out on police or prison facilities within the past month. Congo's police on Saturday said a group of men attacked a police station in Kinshasa, killing at least two.

In May, Christian sect members stormed a prison in Kinshasa, freeing their leader and others. Witnesses say thousands escaped.