While in a camp housing thousands of displaced people just north of Goma, a woman was shot and killed and a number of families forced from their huts, which were then looted by armed men, the UN refugee agency says.
Diplomats admit they do not know where the 2,785 extra troops and 300 police officers will come from, or when they will be sent.
The UN Security Council voted on Thursday for the extra troops and also for the peacekeepers to implement their mandate "in full", through robust rules of engagement.
The Congolese government has welcomed the extra troops for Monuc - the UN mission in DR Congo, but demanded a stronger mandate.
The troops currently have a Chapter Seven mandate - which diplomats describe as robust as it allows peacekeepers to protect the civilian population and themselves - but it also requires them to work with national army - currently in a state of disarray.
"It needs a mandate that is a lot more appropriate to the circumstances on the ground," Communications Minister Lamert Mende Omalanga told the AFP news agency.
Mr Guehenno told the BBC's World Today programme it was of the utmost importance that the troops should be sufficiently resourced.
And unless there was a commitment from Europe, troops were unlikely to be deployed quickly, the former head of UN peacekeeping operations said.
"It's going to be a test of whether the Europeans see Africa as a strategic issue for Europe, as important as Afghanistan - which for me it is - or whether they think it isn't," he said.
On Thursday, the European parliament urged the EU to send special forces to DR Congo.
Most of the UN troops in DR Congo are from India and Pakistan.
They were accused of not doing enough to halt the rebel advance but have stopped them taking the city of Goma - the largest in the region.
BBC Africa analyst Martin Plaut says news of the extra troops and the improved relations between Rwanda and DR Congo have strengthened the hand of UN envoy Olusegun Obasanjo.
The UN has been unable to contain the violence
The presidents of the two countries are reported to be in regular phone contact, he says.
Some diplomats say Rwanda is at the heart of the crisis and the Congolese government has accused its neighbour of backing Gen Nkunda's forces - charges denied in Kigali.
But there are now plans for a joint verification mission to investigate the role of the former Rwandan Hutu forces living in the forests of eastern DR Congo, who participated in the Rwandan genocide, and for joint operations against these rebels.
Gen Nkunda has said he is fighting to protect his Congolese Tutsi community from attack by the Hutu rebels.
Mr Obasanjo is being supported by a nine-strong team including representatives of the African Union, United States and EU, as well as Rwanda and DR Congo.
The rebels withdrew from positions north of Goma on Wednesday - the move came after weekend talks with Mr Obasanjo.
Meanwhile, Congolese President Joseph Kabila is in Angola for talks.
Eyewitnesses say there are Angolan troops are on the ground in North Kivu, deployed to support Congolese army troops - allegations denied by Angolan officials.
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