KINSHASA (Reuters) - The flight of South Sudan’s main opposition leader and more than 750 of his supporters across the border into Democratic Republic of Congo will threaten regional stability if not properly handled, the DRC’s United Nations mission said on Monday.

The mission, known as MONUSCO, said it had rescued another 268 people from Garamba National Park in northeastern Congo over the weekend. They had all fled South Sudan with the country’s former vice-president Riek Machar, following fierce fighting in the capital, Juba.

The Kinshasa government has limited control of Congo’s eastern border regions, which have bristled with militias for decades, and relies on MONUSCO, the world’s largest U.N. peacekeeping mission, for significant security assistance.

“MONUSCO and the United Nations headquarters continue their discussions with the DRC government (and) regional organizations in order to find a favorable resolution to this situation, which could become a threat to peace in Congo and the region,” the organization said in a statement.

But South Sudan accused MONUSCO of taking Machar’s side in the conflict.

Machar, who was picked up by MONUSCO with a leg injury on Aug. 17 and later transferred to Sudan for medical treatment, is the only one of the group known to have left Congo so far.

The most recent transfers bring the total number evacuated by U.N. helicopters to 634. A further 134 people in the park are believed to still require assistance, the statement said.

The transferred fighters are required firstly to hand over their weapons, MONUSCO added.

SOUTH SUDAN IRKED

South Sudanese authorities condemned MONUSCO’s actions.

“The United Nations in Congo has clearly shown that it has taken sides in the conflict by extracting and transporting Machar’s fighters from inside South Sudan to Congo,” South Sudanese presidential spokesman Ateny Wek Ateny told Reuters.

MONUSCO has said it only transported Machar’s supporters from the Congolese side of the border to other Congolese locations for treatment.

The influx of rebel fighters from volatile neighbors is a sensitive theme in Congo, where the flow of Hutu militiamen from neighboring Rwanda after its 1994 genocide helped trigger years of regional conflict in eastern Congo that killed millions.

MONUSCO said in a statement on Sunday that, as of Sept. 8, 117 individuals had been handed over to Congolese authorities while another 183 were being held at two MONUSCO-run facilities.

Congo’s government said it was in talks with South Sudanese authorities over what would happen to the fighters.

Hundreds have been killed in battles that broke out in the world’s youngest nation in July between troops loyal to Machar and President Salva Kiir, his long-time political foe. More than 20,000 South Sudanese refugees have crossed into Congo this year, according to the U.N. Refugee Agency.

Kiir publicly agreed last month to accept 4,000 additional U.N. peacekeepers to the 12,000-strong mission already on the ground but details of the deployment still need to be worked out.