The United Nations expressed deep concern at reports of M23 rebels and Rwandan troops advancing south towards the Congolese city of Bukavu on Thursday, as the militants sought also to assert their control over east Congo's largest city Goma.

The M23 rebels, who said that they captured the city on Monday after a weekslong advance, are one of about 100 armed groups vying for a foothold in mineral-rich eastern Congo. The conflict escalated with the rebels' advance into Goma, which left bodies on the streets and drove hundreds of thousands of already displaced people to flee once again.