"The EU is strongly concerned by recent developments in the Kivus and the deterioration of the security situation," Ashton said in a statement, referring to the country's Nord and Sud Kivu regions.
The 27-nation bloc "strongly condemns the rebellion by some elements within the Congolese army. The EU also condemns the killing of, and all negative impacts on civilians by armed groups, including the FDLR", the Democratic Forces for the Liberation of Rwanda rebel group.
The mutineers, known as the March 23 movement, are former Congolese Tutsi rebels who joined the army under a March 2009 peace deal but defected earlier this year, complaining of poor treatment.
Kinshasa says the mutiny is led by Bosco Ntaganda, a former rebel military chief who had been integrated into the army, and who is wanted by the International Criminal Court for enlisting child soldiers.
Ashton said it was "in the interest of all" that the Democratic Republic of Congo establish its authority over its own territory.
"The current developments require the attention of all countries in the region. Recent cooperation between Rwanda and the DRC on this matter is necessary and positive. The EU is worried by information that this dynamic might be endangered."