A rebel group called the M23 has resurfaced in eastern Democratic Republic of Congo, where it has clashed with government forces.
Military authorities in North Kivu province have accused the M23 of being behind a helicopter crash Tuesday that killed eight UN peacekeepers.
The group has denied downing the aircraft and instead blamed the Congolese army.
Here is background on the M23:
The M23 was born in 2012 among former members of a Congolese Tutsi militia that was once supported by Rwanda and Uganda.
The rebels had been incorporated in the Congolese army under a peace deal signed on March 23, 2009.
Some three years later, they mutinied, saying the deal had not been upheld.
They named their group the March 23 Movement (from which M23 is derived). The organisation is also called the Congolese Revolutionary Army.
The M23 made the world headlines when it briefly seized DR Congo's eastern city of Goma in November 2012.
But a year later, the group was defeated and forced out of the country by a joint UN and Congolese army offensive.
After being defeated militarily, the M23 held talks with Kinshasa while several hundred of its fighters holed up in neighbouring Uganda and Rwanda.
In late 2013, in Nairobi, the M23 and Kinshasa signed an accord that included provisions allowing former rebels to return as a step towards reintegration into civilian life.
Scant progress on this initiative has become a major grievance.
In early 2017, the Congolese government and residents in Rutshuru reported that former M23 fighters had returned to the region. The UN's peacekeeping force Monusco also said it had seen multiple clues of its presence in the country.
The group made an armed comeback last November, accused of staging several raids on military positions around Rutshuru on the edge of the Virunga National Park.
The rebels accuse the Congolese of flouting the 2013 Nairobi accords.
Since the mass arrival in DR Congo of Rwandan Tutsis accused of slaughtering Tutsis during the 1994 Rwanda genocide, Kinshasa has regularly accused Rwanda of carrying out incursions into its territory and of backing armed groups there.
On Monday, the Congolese army accused Rwanda of backing the M23, and claimed to have captured two of the country's soldiers in the combat zone.
Kigali strongly refuted any involvement, saying the men were captured more than a month ago and were not part of its army.
Relations between DR Congo and Rwanda have been tense for more than a quarter of a century. They eased after Felix Tshisekedi became Congolese president in early 2019.
He has met his Rwandan counterpart Paul Kagame several times.
But the M23 resuming its fight has rekindled Congolese suspicion.