The Democratic Republic of Congo government has accused Rwandan forces of joining a new rebel advance in the east of the strife-torn country, in a letter made public Tuesday.
The letter sent by the DR Congo's UN ambassador to the UN Security Council said that "specialized units coming from Rwanda" were supporting M23 rebels battling government forces outside the key city of Goma.
The letter was part of renewed tensions between the neighbours. Rwanda on Monday accused DR Congo and UN forces of shelling two Rwandan border villages.
The M23 rebels launched a new assault outside the North Kivu provincial capital on Sunday and new battles were reported Tuesday.
The DR Congo government says at least 130 people, including 10 soldiers, have been killed in the fighting.
The DR Congo ambassador, Ignace Gatamavita, said there had been "bloody battles" started by the M23 with the Rwandan units against the DR Congo army, the FARDC.
"The M23 rebels and their Rwandan allies attacked, in the early hours of Sunday morning, the positions of the FARDC who had to defend themselves to push back the enemy."
Gatamavita said "this act of provocation" was a breach of a peace and security accord signed by several African countries, including Rwanda, in February.
The accord, under which leaders vowed not to intervene in the affairs of their neighbours, was aimed at ending conflict in eastern DR Congo.
The M23, which UN experts have said receive backing from Rwanda and Uganda, launched an uprising against the DR Congo government last year.
Rwandan diplomats made no immediate comment on the letter.