Insurgents in eastern Congo fired at a United Nations helicopter on Saturday after threatening to attack U.N. aircraft, further raising fears of a return to fighting in the volatile region.
Negotiations between the M23 rebels and the Democratic Republic of Congo's government restarted after U.N.-backed Congolese troops dealt the rebels a rare defeat in August.
But talks have made little progress on ending the latest conflict in a region where fighting, rooted in ethnicity and struggles over resources, has cost millions of lives in the past two decades.
The unarmed U.N. helicopter came under fire as it flew a reconnaissance mission over the M23 stronghold of Rumangabo, in mineral-rich northern Kivu province, the U.N. mission said.
The mission, known as MONUSCO, did not say whether the aircraft had been hit and no injuries were reported.
"M23 rebels will not prevent us from using the Congolese air space," Martin Kobler, the head of MONUSCO, said in a statement. "We shall continue doing all in our power to defend civilian populations including by using force if necessary."
Saturday's incident was the first of its kind since M23 issued a statement earlier this month threatening to destroy any U.N. aircraft flying over territory under its control.
"MONUSCO is a belligerent in this conflict now. It is not neutral. If they want to be part of the conflict we'll take them as part of the conflict," M23 spokesman Amani Kabashi said.
"We only fired warning shots to show MONUSCO that what they're doing is not fair," he added.
M23 launched its rebellion more than a year and a half ago, accusing the government of reneging on promises made in a 2009 peace deal.
It now controls swathes of territory along Congo's border with Uganda and Rwanda - which denies accusations by U.N. experts of supporting the rebel group. Talks have been taking place in Uganda.