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A search is continuing for two British tourists who were kidnapped in a national park in the Democratic Republic of Congo (DRC).

DRC army spokesman Major Guillaume Kaiko Ndjike told Reuters that soldiers had joined rangers in the search operation at the Virunga National Park.

The park's director said the tourists' vehicle was ambushed by gunmen, who killed a ranger and seized the driver.

The Foreign Office said it was supporting the families.

It also said it was in close contact with the DRC authorities.

Local media reports say the ranger shot dead was a female guard, while the UK citizens - who have not been named - were taken along with their Congolese driver.

Park director Emmanuel de Merode told the AFP news agency: "I confirm that our vehicle was attacked. Three people were kidnapped, including two tourists."

The incident took place just north of the city of Goma, North Kivu province.

The ������̳'s Louise Dewast, reporting from the country's capital Kinshasa, said the situation was "very serious".

She said there were armed groups operating in the park and there had been kidnappings before, with half of these involving a ransom.

The national park, which runs along the border with Uganda and Rwanda, covers 3,000 sq miles (7,800 sq km).

It is a Unesco world heritage site and is home to critically-endangered mountain gorillas as well as lions, elephants and hippos.

In April, Mr de Merode, told the ������̳ World Service that recent attacks were part of "a bigger picture which involves the trafficking of natural resources".

He said the park was protected by around 800 rangers but there were also estimated to be between 1,500 and 2,000 militia in and around the park.

There have been a number of killings and kidnappings in recent years.

Five rangers and a driver were killed in the park on 9 April.

A week earlier, a park ranger died in an attack by armed men as he guarded the construction site of a hydroelectric plant.

������̳ Africa editor Will Ross said poachers were active in the park, which was also under threat due to the illegal felling of trees to make charcoal and plans for oil exploration.

Wildlife authorities have tried to protect it but 170 rangers have been killed over the last 20 years, he added.

The Foreign and Commonwealth Office advises against all but essential travel to Goma and has urged Britons not to go beyond the city.

The says tourists are vulnerable if travelling without escorted transport in the eastern part of the country, and the "risk of kidnap or injury as a result of armed or criminal activity remains high".

It said that UK government staff were not always in the area and the British embassy's ability to offer consular assistance could be "severely limited".