"Delighted that two British nationals held hostage in DRC have been released", Johnson posted on Twitter. The Britons were released unharmed, while the driver was injured, the British government said.
A Foreign Office spokesman said: "We are in close contact with the authorities in Democratic Republic of the Congo following an incident involving two British nationals, and our staff are providing support to their families".
Johnson paid tribute to DR Congo authorities and the Congolese Institute for Nature Conservation for their "tireless help".
"We would like to thank our courageous team for ensuring the swift resolution of this incident, and the safe return of the two British nationals", he said.
We wish to extend our deepest condolences to her family and our sincerest gratitude for her bravery and service to Congo.
Cosma Wilungula, director general of the Congolese Institute for Nature Conservation, welcomed the tourists' release. It also covers most of Lake Edward and the Ishasha river valley.
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The park, which is a Unesco world heritage site, is home to critically-endangered mountain gorillas, lions, elephants and hippos.
But it is located in DR Congo's North Kivu province, where armed groups are fighting for control of territorial and natural resources, and poaching is a major threat. The park was renamed Virunga National Park in 1969.
One park ranger was killed during the incident in Africa's oldest national park and three other people, including the British citizens, were abducted.
A female park ranger was killed in the attack, local media reported. In the past 20 years, 175 rangers have died protecting Virunga national park, including five young rangers and a driver killed last month in a militia ambush.
It said that United Kingdom government staff were not always in the area and the British embassy's ability to offer consular assistance could be "severely limited".