Gunmen have kidnapped about 60 people, including eight foreigners, in a remote mountainous region of Peru.
The gunmen raided a camp high in the Andes, which was housing workers who were building a pipeline to carry natural gas.
The gang attacked the camp in the early hours of Monday morning.
Workers from Argentina, Colombia and Chile, as well as three police officers, are among the hostages.
Local media has reported that the kidnappers are demanding a ransom of $1m.
In a live televised address, Peruvian Defence Minister Aurelio Loret de Mola said the government was taking every step necessary to free the hostages, and that the army had been sent in.
He did not say who may have carried out the raid, referring to them simply as "criminals".
A government statement said there were about 60 kidnappers.
There is speculation that the Marxist guerrilla group, the Shining Path, may have carried out the attack. The group has been largely defeated but some guerrillas are still active in the Ayacucho region where the raid took place.
"We are investigating the possibility that this was a Shining Path attack," a local government official said.
The attack targeted a camp housing people working for Argentine petroleum company Techint. It is near Toccate, about 350 kilometres (220 miles) south-east of the capital Lima.
The kidnappers are thought to have escaped to a nearby mountainous enclave known as Vizcatan, along with their hostages and explosives they took from the camp.
Army General Federico Ayarza said 60 soldiers had been flown into the area by helicopter. A further 50 police officers have been sent by road.
In the 1980s, the Shining Path was Latin America's most feared guerrilla group. It was held responsible for sparking off a two-decade long civil conflict in Peru which led to the deaths and disappearances of more than 30,000 people.
The group was dealt a severe blow in 1992 when its leader Abimael Guzman was arrested and sentenced to life imprisonment.
Guzman faces a retrial between September and November after the high court ordered a retrial on the grounds that the 1992 verdict was unconstitutional.