GOMA, (DR Congo): UN investigators said Wednesday they had not ruled out any avenue in a probe into a helicopter crash in eastern DR Congo that killed eight UN peacekeepers, although one lead was a “shining object” that may have caused the incident.

Six Pakistanis, a Russian and a Serb were killed when a Puma helicopter with the UN mission MONUSCO crashed while on reconnaissance over the troubled region on Tuesday. Military authorities in North Kivu province have accused the M23 rebel group of downing the chopper, though the faction denies the charge and instead blames the Congolese army.

“The initial preliminary observations of our force headquarters describe a crash that may have been caused by a shining object,” Khassim Diagne, the deputy special representative for protection and security at MONUSCO, told the French radio station RFI.

The mission’s deputy spokeswoman Ndeye Khady Lo confirmed this account. “The wreckage of the helicopter has been located, an inquiry is underway and should be able to ascertain more about the nature of this object,” she said.

The crash seems to have an “external” cause, she said, but stressed it was “premature” to rule out an accident. Diagne, in his remarks to RFI, said that investigators were not ruling out any scenario, including “an attack”.