A justice official says the inmates, which include many ex-combatants, were freed when gunmen attacked the prison.
Representatives of M23 now appear enthusiastic about achieving a negotiated peace regardless of U.N. plans for eastern Congo.
Urged African leaders to implement a plan to help stabilize eastern Congo.
Rebels declared a cease-fire to permit Ban Ki-moon's visit to proceed.
M23 clashes continued amid U.N. talks over intervention brigade.
The clashes between M23 rebels and the Congolese army have so far kiled 20 people.
Rebels attacked army post near provincial capital of Goma.
Though army as a whole is overstretched and underfunded.
The first step in assembling a new U.N. intervention brigade.
Congolese troops fleeing the M23 rebels last November raped at least 97 women and 33 girls.
