Violent clashes between mutineers and the army in eastern Democratic Republic of Congo (DRC) are hitting aid operations for some 220,000 regionally displaced people, the United Nations said July 11.

The UN's Office for the Coordination of Humanitarian Affairs (OHCA) said it was especially worried after an uptick in violence last week saw Tutsi rebels from the M23 movement seize several towns around Rutshuru in Nord-Kivu.

"Several organisations have had to suspend activities or reorganise their rescue actions, especially in Rutshuru," the UN office said in a statement.

"This is depriving thousands of vulnerable people from the aid they so desperately need."

OHCA called on all fighters to allow humanitarian groups unhindered access.

"The current security situation has not allowed us to calculate the exact number of displaced people, where they are and what their immediate needs are," the OHCA said.

But it estimated that more than 220,000 people had been displaced, including 100,000 in the Rutshuru area.

More than 30,000 more have fled to Uganda and Rwanda.

Between Friday and Sunday, M23 mutineers seized the border town of Bunagana on the Ugandan frontier then took several other towns, though later pulled back.

Some of those who fled their towns have started to trickle home, but Uganda's foreign ministry warned Wednesday the fighting risks destabilising the wider region.

Uganda said it had called for a special meeting of the International Conference on the Great Lakes Region to discuss the crisis, which will meet on the sidelines of the African Union summit beginning Sunday.

There are growing fears that M23 may now target the Nord-Kivu provincial capital of Goma and a UN official in New York said Kinshasa was moving a US-trained battalion from the north of the country to defend the city.

The UN mission in DR Congo, known by the acronym MONUSCO, is also moving troops and Special Forces from its 18,000-strong peacekeeping force to the city, the official said.

"The UN mission is doing its utmost in coordination with the Congolese army to protect civilians," MONUSCO head Roger Meece was quoted as saying by the UN spokesman.

Meece also "voiced his concern about continuing reports that M23 mutineers are receiving external support and are well-armed, trained and equipped," the spokesman added.