Forces of the Democratic Republic of Congo were losing control of the key city of Goma on Wednesday after rebel groups backed by Rwanda took over the airport and shared plans to set up a new administration.

A rebel alliance claimed the capture of the biggest city in the Democratic Republic of Congo’s mineral-rich eastern region this week, pushing back against resistance from government troops backed by regional and UN intervention forces.

The Democratic Republic of Congo’s government says the Rwanda-backed rebels’ advance constitutes a “declaration of war."

The M23 militia, funded and directed by Rwanda, said it had seized the city of Goma, terrifying its people, many of whom sought shelter there after fleeing the rebel advance.

Thousands fled the city of Goma on Monday as fighting raged between Congolese forces and rebels backed by neighboring Rwanda, who claimed to have captured eastern Congo’s largest regional hub. Pockets of chaos and gunfire had some people hunkering down as the rebels marched into the city with a population of about 2 million.

By Yassin Kombi and Sonia Rolley GOMA, Democratic Republic of Congo (Reuters) - Rwandan-backed rebels strengthened their control over east Congo's largest city, Goma, on Wednesday as columns of Romanian mercenaries hired to fight for Congo entered Rwanda under tight supervision by Rwandan security forces.

Rebels backed by Rwanda captured more towns in eastern Congo on Wednesday, as fighters moved beyond the key city of Goma in an apparent attempt to expand their control in the conflict-battered region.

Fighting between Rwanda-backed rebels and the Congolese army continued for a second day in Goma on Tuesday amid calls by African leaders for an immediate ceasefire.

By Yassin Kombi and Sonia Rolley GOMA, Democratic Republic of Congo (Reuters) -The United States told Rwanda it was "deeply troubled" by the fall of Goma in eastern Congo to Rwandan-backed M23 rebels,