Democratic Republic of Congo forces have attacked Ugandan Islamist rebels in the lawless east of the country.
The UN-backed offensive has been launched to clear insurgents from the mineral-rich zone.
Congolese government troops moved in on positions held by ADF-NALU rebels who have been based in Congo for years and are seen as a major obstacle to peace.
The Ugandan government has said the group is allied with Somalia’s al Qaeda-linked al Shabaab movement. The nature of these ties is not clear, despite their clear Islamist ideology.
Congolese officials hold the group responsible for a spate of attacks including a massacre of 21 villagers in eastern Democratic Republic of Congo.