The crew members had been seized alive and handed over to the M23 movement's military chief, Sultani Makenga, the army's General Leon Mushale told reporters in the eastern city of Goma.

Mushale said the fourth crew member was still missing.

The incident could point to a resurgence in activity by M23 fighters more than three years after the group was crushed by the army, and herald renewed instability in eastern Congo where dozens of armed groups are fighting for control of mineral resources.

Elie Mutela, a senior representative of M23's political wing based in Uganda, denied its fighters were in Congo.

Opponents have accused the government of exaggerating a revival of the M23 rebel group in order to deflect attention from President Joseph Kabila, who remains in power after the official end of his mandate.

There have, however, been persistent reports of renewed M23 activity.

Makenga fled with hundreds of his men to Uganda in November 2013 after his forces were routed by Congolese and U.N. troops, ending a two-year insurgency during which they controlled huge swaths of eastern Congo and briefly captured Goma.

He had been under watch by Ugandan security forces in the Ugandan capital, Kampala, but a Ugandan army spokesman on Tuesday told Reuters that Makenga was "missing".

Fighters loyal to Makenga were held in camps for demobilized fighters after their 2013 defeat, though Congolese officials said earlier this month that a number had crossed back into Congo.

Uganda was accused by U.N. experts of helping to arm the M23 rebels during their insurgency, allegations which Uganda strongly denied.