"It is with sadness and anger that I have just learned of the deaths of peacekeepers in an ambush near Beni," a trading hub in the north of troubled North Kivu province, Kobler said yesterday on his Twitter account, without stating the number killed.
Kobler told AFP he "firmly condemned these attacks against the Blue Helmets", adding that an investigation was under way and the death toll was as yet unknown.
He said the attack occurred around Oicha, some 20 kilometres (12 miles) north of Beni.
Earlier yesterday, a DR Congo military spokesman said army troops killed 16 ADF rebels in two days of clashes in the region.
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It said four soldiers died in the fighting, while a civil society source said 28 soldiers were killed, 22 wounded and eight captured.
Kobler issued a statement Monday after a UN helicopter came under fire by "unidentified armed men" near Oicha.
Most of the victims were hacked to death, in atrocities that prompted a joint operation by the Congolese army and UN troops to put down the jihadist fighters in December.
A degree of calm was restored, but the combined intervention failed to bring a halt to the killings of civilians, which spread northwards to Orientale province.
Since January 1, at least 60 people have lost their lives across the region.