Eight UN peacekeepers have been killed in clashes in eastern Democratic Republic of Congo, the UN says.
The Congolese army is working with UN troops in eastern DR Congo
The Guatemalan special forces members were killed when they met a group of Ugandan rebels in a national park.
They had been looking for fighters from the Lord's Resistance Army, accused of carrying out atrocities across northern Uganda and in southern Sudan.
The UN and the Congolese army are trying to rid numerous armed groups from eastern DR Congo before elections.
The latest clash took place in the Garamba National Park on the border with Sudan, according to the UN.
"The unit which was conducting an operation in this area established contact with rebel elements at 6 a.m. There followed an exchange of fire lasting four hours, requiring the intervention of armed helicopters," the UN statement said.
A UN military spokesman said at least 15 LRA fighters were killed, out of a group estimated to number 50 or 60.
Five members of the peacekeeping force were injured in the incident and were flown to hospital in Bunia, several hundred km south of the park.
UN spokesman Kemal Saiki said the deaths would not deter the peacekeeping mission.
"We are determined to stay the course," he told the AP news agency.
"And anyone who thinks we're going to give up is seriously mistaken."
Some 20,000 people crossed into Uganda to escape separate fighting in the area over the weekend, says the UN High Commissioner for Refugees (UNHCR).
Some 15,000 UN troops are stationed in DR Congo: the world's largest peacekeeping force.
The east has been out of the control of central government for many years.
Despite an official end to the civil war in 2003, bands of militia groups still terrorise civilians and exploit the region's minerals and timber to finance their operations.
Several neighbouring countries were drawn into DR Congo's brutal five-year conflict which led to some 3m deaths.
DR Congo's first multi-party elections in four decades are due on 29 April.