Geneva ? About 20,000 people have fled violence in Congo to seek refuge across the border in Uganda over the last four days, the U.N. refugee agency said Sunday.

In eastern Congo, home to many of the refugees, renegade former army soldiers ambushed U.N. peacekeepers with mortars in a hilltop banana plantation Sunday, sparking a firefight that left four attackers dead, U.N. officials said.

The peacekeepers were trying to flush the former soldiers out of territory they captured during raids this week, U.N. military spokesman Mayank Awasthi said. The raids in eastern Congo’s North Kivu province forced the refugees to cross the nearby border with Uganda.

Congo is struggling to recover from back-to-back wars. The first was in 1996-1997 when Rwandan-backed rebels swept the country to overthrow dictator Mobutu Sese Seko. A second 1998-2002 war sucked in the armies of half a dozen African nations.

Major fighting ended in 2002, but the situation in Congo remains dire because of poor access to health care, inadequate international aid and continued insecurity. The problems are particularly acute in eastern Congo.