Mr Miliband will visit DR Congo and Rwanda
Foreign Secretary David Miliband has flown to the Democratic Republic of Congo, amid fierce fighting between government and rebel forces.
He and his French counterpart Bernard Kouchner are to visit Rwanda to impress on both countries the need to find a solution "urgently".
More than 200,000 people are estimated to have been forced from their homes since fighting resumed in August.
The Tories and Lib Dems say UN forces should be strengthened in DR Congo.
A tense ceasefire is holding in the eastern city of Goma, from which thousands of people fled as rebels advanced on Wednesday.
But the UN refugee agency, the UNHCR, says it has credible reports that camps sheltering 50,000 displaced people in the eastern DR Congo have been destroyed.
Rebel leader General Laurent Nkunda says he is fighting to protect his Tutsi community from attack by Rwandan Hutu rebels, some of whom are accused of taking part in the 1994 Rwandan genocide.
It has been alleged that the Rwandan government has given him some support, which it strongly denies.
The European Union has been trying to bring Rwandan president Paul Kagame and Congolese president Joseph Kabila together.
Mr Miliband and Mr Kouchner are expected to urge both not to support forces involved, said the BBC's world affairs correspondent Mike Wooldridge.
A Foreign Office spokesman said: "They will impress upon the leaders of both countries the seriousness of the situation in eastern Democratic Republic of Congo - the need to engage urgently to find a solution to the underlying problem and to take stock of the situation as they find it."
He added: "They're not going to set unrealistic ambitions for the visit but the fact that they are going illustrates the level of concern that we and the French have."
Earlier International Development Secretary Douglas Alexander announced an extra £5m for aid for the country to ensure people had food, water and shelter. The UK already provides £42m to DR Congo each year.
For the Conservatives, Andrew Mitchell called for the UN mission in the African nation - already the biggest peacekeeping force in the world with 17,000 troops - to be increased.
He told BBC Radio 4's World at One programme that the UN force was outgunned in Goma by the 8,000-strong group of FDLR rebels.
"Unless the UN is reinforced, it is simply not going to be able to tackle this problem," he said.
He said the UN had not yet delivered on a Security Council resolution passed in March to deal with the situation in Goma.
"It is a matter of ensuring that the will of the international community and the participants, as expressed through these different agreements, is enforced on the ground."
For the Liberal Democrats, Edward Davey said the UN mission in DR Congo had been "starved of resources for far too long, making a difficult job impossible".
"Britain, with our allies, should either contribute resources or help African countries who have the troops but not the cash," he added.
Oxfam has removed its international staff from Goma as a "precautionary measure" and Save the Children began the evacuation of its staff in the North Kivu province because their lives were threatened, it said.
Aid agencies say the situation in and around Goma remained highly volatile with access to those in need extremely difficult.
The UN High Commissioner for Refugees said there were reports that the camps north of Goma had been forcibly emptied, looted, and burned.