Rebels in eastern areas of the Democratic Republic of the Congo have advanced even further towards the city of Goma after four days of clashes.
They have pushed back government troops and U.N. peacekeepers who are based in what is the capital of North Kivu. It is also the headquarters of the U.N. peackeeping mission in the region and has about 6,700 forces based there.
Goma, on the Rwandan border, is home to one million people including hundreds of thousands displaced by conflict.
The M23 rebels deserted government ranks earlier this year, accusing Kinshasa of failing to respect a 2009 peace deal which ended a previous rebellion in North Kivu.
Congo's government and U.N. investigators have accused Rwanda of supporting the group.
More than 5 million people are estimated to have died from violence, hunger and disease in wars in the Democratic Republic of the Congo since 1998.