Columns of M23 fighters allied with Rwandan troops on Sunday entered the centre of another key city in eastern Democratic Republic of Congo as the African Union highlighted growing fears that the strife-torn country could break up.

The armed group reached outlying districts of Bukavu, capital of South Kivu province, on Friday, shortly after taking control of its airport about thirty kilometers (18 miles) away.

The fall of the city of one million people, which was barely defended by the Congolese armed forces (FARDC), gives the M23 total control of Lake Kivu, following its capture of Goma, capital of the neighboring province of North Kivu, at the end of January.

Growing international calls have been made for Rwanda to end its military backing for M23.