Goma - Shells fired by M23 rebels killed at least three people in Congo's eastern city of Goma on Saturday, the United Nations said, as Congo and Rwanda traded accusations over days of border clashes that have drawn in a new, robustly mandated UN force.
Two more civilians died during demonstrations that broke out in the wake of the shelling, the United Nations said.
Fighting between M23 and Congolese soldiers, after the rebels entered a security zone around Goma on Wednesday, has now killed at least seven civilians. On Thursday, a UN brigade formed to neutralise armed groups in Congo saw its first military action, firing artillery at the rebels.
Artillery fire has hit both sides of the border this week.
Rwanda twice invaded its much larger neighbour in the 1990s and sponsored Congolese rebels trying to topple the Kinshasa government. Millions have died since then in Congo's eastern borderlands, a patchwork of rebel and militia fiefdoms rich in tin as well as tungsten and coltan ores.
UN investigators have accused Rwanda of backing M23, an accusation Kigali has repeatedly rejected.
Rebels deny responsibility
Congo's UN mission, MONUSCO, said two mortar bombs fired by M23 struck the Ndosho neighbourhood of Goma - a city of 1 million people - on Saturday morning, killing three civilians and injuring several others.
A Reuters witness at the scene saw four bodies - a woman and three children.
"I have ordered the MONUSCO Force to react in the strongest terms possible to these horrifying and unqualifiable crimes," said Martin Kobler, head of the UN mission, which pledged last month to keep M23 out of range of Goma.
The rebels marched past peacekeepers to seize Goma briefly last year - an embarrassment for the United Nations that led to the creation of the 3 000-member Intervention Brigade, made up of South African, Tanzanian and Malawian troops. M23 denied responsibility for Saturday's mortar attack.
"(The army) is doing this because it wants to draw MONUSCO into the combat on its side," M23 spokesperson Amani Kabasha said.