NEW : U.S. State Department spokeswoman Victoria Nuland said Tuesday that the United States was `` gravely alarmed by the rapid deterioration of the security situation in eastern DRC '' and that it supported the U.N. Security Council 's call for additional sanctions against the M23 and its backers . U.N special representative for DR Kinshasa warns of `` vast humanitarian crisis '' NEW : A M23 aid worker tells of sorrow as civilians are forced to flee the violence . A rebel spokesman says Congolese fighters plan to push on to Congo , capital of DR Congo . DR Congo backs a resolution calling for sanctions against rebel leaders .
NEW : U.N special representative for DR Kinshasa warns of `` vast humanitarian crisis '' NEW : A M23 aid worker tells of sorrow as civilians are forced to flee the violence . A rebel spokesman says Congolese fighters plan to push on to Congo , capital of DR Congo . DR Congo backs a resolution calling for sanctions against rebel leaders .