Goma - Shelling killed two people Saturday in Goma in the restive east of DR Congo after a newly-formed UN brigade took its first military action to back government troops and prevent rebels from entering the mining hub.
It was unclear who fired the shell that smashed into Goma's western neighbourhood of Ndosho, sparking an angry reaction from residents who blocked access to vehicles, witnesses said.
"A shell has just landed on my neighbourhood," Ndosho resident Charles Paluku told AFP on the phone, adding that two people had been reported dead as a result of the explosion.
Another witness speaking on condition of anonymity provided the same death toll and said the shell had struck near Ndosho's Saint-Francois Xavier church.
"I understand the population's frustration," Prosper Basse, a spokesperson for the UN peacekeeping mission, said in reaction to reports that Ndosho residents had staged an impromptu demonstration to protest against the violence.
Residents said two other shells were fired in the Goma area on Saturday, including one that crashed into the Mugunga 3 camp for displaced people, a few miles west of the city.
There were no immediate reports of any casualties from those shells.
In open letter sent to UN Secretary-General Ban Ki-moon, M23 rebel leader Bertrand Bisimwa accused Kinshasa on Saturday of targeting civilians and demanded an independent inquiry into its actions.
"The Congolese government decided to shell the town of Goma causing the deaths of men and creating a climate of despair among residents," he wrote in a document seen by AFP.
The M23 was founded by former fighters in a Tutsi rebel group whose members were integrated into the regular army under a 2009 peace deal that they claim was never fully implemented.
Several of its leaders have been hit by UN sanctions over alleged atrocities and the world body has accused Rwanda of arming - and even of commanding - the rebels, a claim Kigali denies.
The M23 rebels briefly seized the mining hub of Goma last year and only pulled out following a regionally-brokered deal, under which they were supposed to remain in positions several miles outside the city.
Fighting has erupted sporadically since mid-July, ending a two-month lull in the violence, and the rebels moved closer to Goma, arguing that Kinshasa was reneging on its pledge to hold direct talks.
The group has threatened to recapture Goma but UN forces, including a 3 000-strong intervention brigade with a robust mandate, have moved in to create a security zone around the provincial capital.
Following a fresh deadly bout of fighting that erupted on Wednesday, the UN brigade formed to eradicate armed groups in the region launched its first military action against the M23, fighting alongside the FARDC.
The brigade, the first with an offensive mandate to battle the dozens of armed groups operating in the region, is made up mainly of troops from southern Africa.
Rwanda, which accused Congolese troops of firing a rocket and mortar shells over the border over the past 48 hours, warned on Saturday that it will not stand by "indefinitely".
"The RDF [Rwanda Defence Force] remains prepared to take all necessary measures to ensure the safety of the population," Rwanda's army spokesman Joseph Nzabamwita said in a statement.
Kinshasa had also accused Rwanda of firing rockets on Goma on Thursday.
Eastern DRC, which borders Rwanda and Uganda, was the cradle of back-to-back wars that drew in much of the region from 1996 to 2003 which were fought largely over its vast wealth of copper, diamonds, gold and coltan, a key mobile phone component.
The instability there was exacerbated by the aftermath of the Rwandan genocide, when Hutus implicated in the killing of some 800 000 mostly Tutsi victims fled across the border after Tutsi leader Paul Kagame came to power.