The United Nations mission in Congo says it has spotted fresh camps and well-equipped soldiers it believes are from Rwanda's armed forces.
A mission spokesman says the fighters were sighted in new aerial photographs taken in eastern Congo.
Wednesday, U.N. officials in Congo reported sighting 100 fighters believed to be Rwandan troops.
Rwanda's government has refused to confirm or deny sending its troops into Democratic Republic of Congo.
Rwandan President Paul Kagame has said any invasion into Congo would target Rwandan Hutu rebels and not Congolese forces. He has blamed the Congolese government and the United Nations for failing to disarm Hutu militiamen who fled across the border after perpetrating Rwanda's 1994 genocide.
The U.N. Security Council is due to hold an emergency session Thursday to discuss the crisis.
The United States and the European Union are calling on Congo and Rwanda to resolve the situation diplomatically.
Some information for this report provided by Reuters and AP.