Washington - The US State Department late on Tuesday said that Washington is "gravely alarmed" by the speed at which security is deteriorating in the Democratic Republic of Congo.
Rebels in the DRC seized the key eastern city of Goma amid warnings of a humanitarian catastrophe and reports of killings, abductions, looting and extortion of civilians.
Locals however cheered and applauded as rebels drove around downtown Goma after fighters of the M23 movement marched into the city facing little resistance.
"The United States is gravely alarmed by the rapid deterioration of the security situation in eastern DRC," State Department spokesperson Victoria Nuland said in a statement.
"We condemn the renewed military campaign by the M23 rebel group, which is an affront to the sovereignty and territorial integrity of the DRC and in violation of international law."
The United States, Nuland said, calls "for a ceasefire, and for the M23 to return Goma to DRC authorities and pull back to their July positions."
The rebels have been blamed for hundreds of deaths since they launched their uprising in April. UN experts have accused neighboring Rwanda and Uganda of backing the M23, a charge both countries deny.
Nuland also called "upon all states to use their influence on the M23 to bring about an immediate end to the hostilities."
She added: "We believe it is critical that any resolution to the crisis include holding the M23 leadership accountable for their human rights abuses and violations of international humanitarian law."
The M23, formed by former members of an ethnic Tutsi rebel group, mutinied in April after the failure of a 2009 peace deal that integrated them into the regular army.
The Tutsis are the minority ethnic group of Rwandan President Paul Kagame and the target of the 1994 genocide in that country that claimed an estimated 800 000 lives.