Residents of the besieged city of Goma, in the east of the Democratic Republic of Congo, say they are gripped by fear as gunshots continue to ring out around their homes, days after rebel forces claimed they had taken over.

Residents of eastern Congo's largest city of Goma greeted the arrival of Rwanda-backed rebels with trepidation on Monday, some staying indoors and others coming out to cheer in what one called a "show" of happiness.

Rwanda-backed rebels captured large parts of Goma, the biggest city in eastern Congo, including its airport, the United Nations said, as Rwanda's president on Wednesday joined calls for a ceasefire in the decadeslong conflict amid mounting international pressure.

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.

Rwanda, which diplomats say backs M23 fighters who seized Goma in Democratic Republic of Congo this week, called on Wednesday for a ceasefire across eastern Congo and for Congo to negotiate with the rebels while denying Rwandan troops were involved.