Amateur videos filmed at an eastern DRC border post and shared on social media show armed troops, in uniforms with Ugandan flags on the sleeves, as they advance on foot under local people's gaze.

"The first Ugandan troops have entered the DRC" at the Nobili border crossing in North Kivu state, a United Nations source told AFP on condition of anonymity.

The source added that the soldiers were heading for Kamango, around eight kilometres (five miles) from the frontier.

"Ugandan soldiers were arriving on foot at the Nobili border post all day," said an aid worker on the scene who also requested anonymity.

"From 4 pm (1400 GMT) a column of troops entered Congolese territory. I couldn't count how many, but there are a lot of them," he added.

"It's a column of very well-armed troops on foot, followed by armoured vehicles."

Neither Kinshasa nor Kampala have officially confirmed the arrival of Ugandan troops in the DRC.

But Ugandan army spokeswoman Flavia Byekwaso said in a statement that "targets were accurately hit" in bombardment earlier Tuesday.

"Operations against the terrorists will continue as we look for other targets of opportunity during ground operations," she added.

"I can confirm that after the air strikes ground operations will follow. There are going to be ground troops moving in," Byekwaso told AFP.

Tuesday's strikes were against the ADF, an armed group accused by Kinshasa of civilian massacres in the country's east and blamed by Uganda for attacks claimed by the Islamic State jihadist group.