Crowds of Congolese police officers who switched to the M23 rebel group sang and clapped in occupied Bukavu city on Saturday, preparing for retraining under the authority of the Rwandan-backed rebels who are intent on showing they plan to stick around and govern.

Rwanda-backed rebels have captured two key cities in Congo’s mineral-rich east in less than a month after a major escalation in their yearslong fighting against overstretched and weakened Congolese forces.

The U.N. Security Council unanimously adopted a resolution Friday demanding that the M23 rebels in eastern Congo immediately cease hostilities and withdraw from territories they have seized. The council also threatened sanctions on those who prolong the conflict.