By Yassin Kombi and Sonia Rolley GOMA, Democratic Republic of Congo (Reuters) -President Paul Kagame said Rwanda was ready for "confrontation" as he rejected criticism over his backing for M23 rebels who were pushing south on Thursday in eastern Democratic Republic of Congo after capturing the major city of Goma.

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.

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 has vowed “a vigorous and coordinated response” against a rebel alliance that has besieged swaths of the nation’s mineral-rich east and forced hundreds of local troops and foreign mercenaries to surrender.

The Rwandan-backed M23 rebels have released captured Romanian mercenaries who were fighting with the Congolese army. As they passed a border, they were chastised by Willy Ngoma, who tapped them mockingly one by one.

Rwanda-backed rebels claimed they captured eastern Congo’s strategic city of Goma, the hub of a region containing trillions of dollars in mineral wealth that remains largely untapped, the Associated Press reported.

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.

GOMA, Democratic Republic of Congo - 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,

Rwanda's ally Uganda, unhappy about another rebel group in DR Congo that threatens its security, has also been accused of helping the M23 - with its officers also spotted at Tchanzu. The UN experts say Uganda has also supplied weapons, hosted rebel leaders and allowed cross-border movements of M23 fighters - accusations Kampala denies.

Congo's security forces are fighting against Rwanda-backed rebels who advanced into a key eastern city in a major escalation of a decadeslong conflict.

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.