More than 700 women, men and children were raped when Angola expelled thousands of people back to Democratic Republic of Congo over the past two months, the UN said.

One woman died in hospital from injuries suffered in a sex attack, according to an aid group working in DR Congo and a top UN official made a new call for an urgent inquiry into the rapes.

An estimated 7,000 people have arrived in DR Congo in the past two months after being expelled by Angola, which accused them of being illegal migrants, according to latest UN Office for the Coordination of Humanitarian Affairs (OCHA) figures.

Humanitarian groups reported 6,621 people in Western Kasai province and 322 in the Tembo area of Bandundu province, an OCHA statement said.

Non-government groups first warned the UN about the rapes on October 23.

Aid workers have said more than 600 people in Western Kasai allege they suffered sexual violence, according to the statement. A special mission is visiting the region this week.

A humanitarian agency mission which went to Tembo has found that 99 women and 15 men had been victims of "sexual violence," it said.

"One woman died in hospital due to the violence suffered," Francesco Mazzarelli of the Italian aid group CISP said in the statement.

"These allegations of abuse need to be investigated as a matter of urgency," said Valerie Amos, UN under secretary general for humanitarian affairs and UN emergency relief coordinator.

In October 2009, the two countries expelled tens of thousands of people in both directions. Many became stranded on the border without food and shelter.