UN chief Ban Ki-moon has begun a trip to the Democratic Republic of Congo as fighting continues near the eastern city of Goma.
Mr Ban said he was deeply concerned by the renewed fighting and said the world community would stand with Congo.
In the latest violence, rebels fired two rockets at Goma killing one person and wounding four, officials said.
Earlier, the World Bank unveiled a $1bn (£660m) aid package to help DR Congo and its neighbours.
World Bank head Jim Yong Kim, who is also visiting Congo, said the money would be used for health, education, cross-border trade and hydroelectricity projects.
Government and M23 rebel forces have been involved in heavy fighting near Goma since Monday.
"We are in a very crucial and important timing," UN Secretary General Mr Ban told reporters in the capital Kinshasa.
"The Security Council recently strengthened the mandate and role of the United Nations peacekeeping mission (Munusco) with the introduction of an intervention brigade. This is again an unprecedented one and I am sure that this will bring peace and security at this time."
An estimated 800,000 people have fled their homes since the M23 launched its rebellion last May.
UN peacekeeping officer Col Premanku Ghosh said two rockets had exploded in Goma's Ndosho neighbourhood on Wednesday and that civilians were among the casualties.
Announcing the aid package, Jim Yong Kim said the new funding could be "a major contributor to a lasting peace."
The package is to support a peace deal signed in February between DR Congo and its neighbours, some of whom are accused of backing the rebels.
The largest tranche of the aid - $340m - will go towards an 80-megawatt hydroelectric project in Rusumo Falls, providing electricity to Burundi, Rwanda and Tanzania.
Despite its vast mineral wealth, decades of conflict and mismanagement mean most Congolese remain stuck in poverty.
Mr Ban and Mr Kim are also due to visit Rwanda and Uganda.
Last year, a UN report accused the two countries of backing the M23, an allegation they denied.
-BBC
