The United Nations and Democratic Republic of Congo have used helicopter gunships to attack army mutineers thought to be threatening the main eastern city of Goma.
Three helicopters from the UN country mission and two from the DRC army (FARDC) were seen around the villages of Nkokwe and Bukima on Thursday.
The UN and the Congolese army sent MI24 and MI25 helicopters flown by Ukrainian pilots. The gunships, first made by the Soviet Union, strafed hillsides with 30mm rounds and fired rockets, a UN source said.
"We made several passes on rebel positions," the UN official said.
The UN and the troops from the Democratic Republic of Congo, which claims the rebels are a Rwandan proxy, had earlier deployed tanks around Goma in Nord-Kivu province.
However, the M23 rebels said they had no plans to seize the regional capital and only wanted to negotiate with the government in Kinshasa.
"The FARDC are currently attacking our positions, but they don't know where we are. There's no problem," a colonel from the rebels told AFP.
The M23 rebels - named after a failed 2009 peace deal signed on March 23 - are led by Bosco Ntaganda, nicknamed the Terminator, who is wanted by the International Criminal Court for recruiting child soldiers a decade ago.
His co-accused and former boss Thomas Lubanga was sentenced to 14 years in jail on Tuesday.
The mutineers are ex-rebels who were integrated into the regular army in 2009 as part of a deal that followed their failed 2008 offensive on Goma, under the command of Tutsi leader Laurent Nkunda.
They defected in April, ostensibly over pay, but experts argue Ntaganda and his men are flexing military muscle to clinch further rights over the area's lucrative mines.
The UN's mission in DR Congo, MONUSCO, is one of the largest UN peacekeeping operations.