By Yassin Kombi and David Lewis GOMA, Democratic Republic of Congo (Reuters) -As an East African bloc urged an immediate ceasefire in eastern Democratic Republic of Congo, Rwandan-backed M23 rebels who seized the city of Goma extended their advance on Wednesday,

Democratic Republic of Congo President Felix Tshisekedi said Wednesday that the international community's failure to respond to the worsening security crisis in the country's east was "an affront",

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.

Democratic Republic of Congo President Felix Tshisekedi, speaking publicly for the first time since Rwandan-backed rebels seized the eastern city of Goma, said his government was preparing a response and warned of “unpredictable consequences” for the region.

Many Congolese see the rebel advance as an invasion of their country by a foreign power in an attempt to seize land and Congo’s valuable rare minerals.

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.

DR Congo's President Felix Tshisekedi insisted Wednesday that his troops were mounting a "vigorous" military response as Rwanda-backed fighters advanced in the east of the country.

The rebels, which Rwanda denies supporting, have long been funded at least in part by the illicit mineral trade.

M23 rebels in the Democratic Republic of Congo have seized Goma and are advancing towards Bukavu, amplifying tensions in the region. The conflict, fueled by resource control, has overwhelmed local hospitals and forced Romanian mercenaries to withdraw.

Rwandan backed rebels have entered the city of Goma, a key city in neighboring Democratic Republic of Congo. Could the mineral rich region be in danger of tipping into all out regional conflict?

United Nations chief Antonio Guterres on Sunday urged Rwanda to withdraw its forces from the eastern Democratic Republic of Congo where fierce fighting raged as Kigali-backed fighters closed in on the major city of Goma.