GOMA, Democratic Republic of Congo (Reuters) -Congolese M23 rebels entered the centre of the eastern city of Goma on Monday, two witnesses said, hours after they claimed to have seized the city despite the United Nations Security Council demanding an end to the offensive.

Congolese rebels and allied Rwandan forces entered the outskirts of Goma on Sunday and the airport in the key eastern city was no longer in use, the top UN official in the country said. Thousands fled the fighting that also killed at least 13 peacekeepers.

Tens of thousands of people are fleeing towns in the Democratic Republic of Congo's east, as rebel forces close in on the city of Goma. Explosions and gunshots were heard in city - home to more than a million people - late on Sunday evening, according to local media reports.