The Democratic Republic of Congo (DRC)'s military has been shelling positions it believes are held by rebels who have been fighting the army for weeks in the country's east.

The rebels are fighters who were integrated into the national army under a 2009 peace deal, but who later defected, complaining of poor conditions.

The fighting since late April has driven tens of thousands of people to flee to neighbouring countries, including Uganda.

Security sources say the government troops are advancing, isolating the mutineers - now understood to number about 300 fighters hiding in forested hill country - yet residents are suffering, and fear there is worse to come.

In an exclusive report, Al Jazeera's Malcolm Webb visits Bunagana, a strategically important town in the east of the DRC, key to controlling border crossings into Uganda.

The military has been fighting the mutineers since late April, first in Masisi territory, northwest of the provincial capital of Goma, and later in Rutshuru, where the dissidents fled and regrouped.

The mutineers, who began defecting in early April, have formed a new military group called the March 23 Movement (M23), comprising of former members of the rebel National Congress for the Defence of the People (CNDP).

Former CNDP commander Bosco Ntaganda is accused of leading the mutiny.

Ntaganda, known as "The Terminator", is wanted by the International Criminal Court on a war crimes charge of enlisting child soldiers.