The Democratic Republic of Congo's foreign minister on Friday accused Rwanda of illegally occupying part of its territory, after the M23 rebel group captured the eastern Congolese city of Goma.

U.S. Secretary of State Marco Rubio called for a urgent cease-fire in the conflict in eastern Democratic Republic of Congo saying Washington was "deeply troubled" by a recent escalation in the fighting.

Rwandan-backed M23 rebels say they are now in control of the key eastern Congolese city of Goma. Their fighters continue to claim more territory in one of the world's most mineral-rich territories.

In 2012, when M23 rebels appeared poised to seize control of a major city in eastern Congo, western countries suspended aid to put pressure on Rwanda to withdraw its support.

A conflict that has raged for decades reached a flashpoint this week when rebels backed by Rwanda marched on a key Congolese city in a bid to occupy territory and exploit minerals.

Britain has warned Rwanda that its involvement in an escalating conflict in the Democratic Republic of Congo could jeopardise the over $1 billion of aid it receives every year.

Rwanda's government, led by President Paul Kagame, has been accused by the DRC and various international organizations of supporting M23, including providing military assistance, training, and logistical support.

As Rwanda-backed M23 rebels in eastern Democratic Republic of Congo push south towards the city of Bukavu, they are likely to have to fight their way through thousands of troops from Burundi, ramping up the risk of a return to full-blown regional war.

Critical minerals factor into the fight.

The Rwandan-backed armed group M23 moved south as it closed in on a key military airport in DR Congo on Friday, a day after pledging to take the capital Kinshasa and as international criticism mounted.

By Yassin Kombi and Sonia RolleyGOMA, Democratic Republic of Congo (Reuters) - Rwandan President Paul Kagame blasted criticism of his country's role in eastern Democratic Republic of Congo where rebels his government backs have seized its largest city,