Rwanda-backed rebels have captured two major cities in Congo’s mineral-rich east after a major escalation in their yearslong fighting against Congolese forces.

Rwanda-backed rebels appeared to be heading toward a third major city in eastern Congo, residents said Tuesday, as international pressure rose over the M23's expansion in a mineral-rich region that’s critical for global technology.

Analysts say the deadly march by Rwanda-backed rebels across eastern Congo could widen into a regional conflict drawing in even more countries, and two neighboring nations with the most involvement in the mineral-rich area might be the key to stopping the violence.

The U.N. human rights chief accused Rwanda-backed rebels who seized a second major city in eastern Congo of killing children and attacking hospitals and warehouses storing humanitarian aid.