At least 26 tourists have been kidnapped by armed rebels in north-western Colombia, the authorities say.

The tourists, mostly from the southern city of Cali, were travelling through the Utria national park when heavily armed men stopped their bus, according to reports from the region.

They were taken to a beach in a jungle area and at that point their trail disappeared

Colombian Interior Secretary Narvy Yugarqui

Police have blamed the National Liberation Army - ELN, Colombia's second-largest left-wing rebel group - for the mass abduction.

Both the ELN and its bigger rival the Revolutionary Armed Forces of Colombia rely heavily on kidnap ransoms to pay for their operations.

The tourists were on a fishing trip, in a region renowned for its spectacular coastline, when they were abducted.

"They were taken to a beach in a jungle area and at that point their trail disappeared," Colombian Interior Secretary Narvy Yugarqui said.

Remote area

It is the second kidnapping incident in the region in a week.

Uribe; determined to crack down on the violence

On Monday another 12 tourists, most of them teenagers, were taken hostage at La Fortuna, 100 kilometres (60 miles) north of Utria National Park.

The park was once promoted as an eco-tourism destination - but visitors have dwindled as rebel kidnappings increased.

The government has sent troops to the region to hunt down the guerrillas.

However the area is densely forested which could make any rescue attempt difficult

Colombian rebels carry out hundreds of kidnappings every year to help finance their fight against the government, and they provide as much as 40% of their income.

Newly-elected Colombian President Alvaro Uribe has vowed to crack down on rebel groups.