Four Chinese oil company employees held hostage since June 2011, allegedly by Colombia's FARC rebels, have been freed in southern Colombia, their embassy said Thursday.

"They released the four last night in the department of Caqueta. They are in good spirits," said the spokesman of China's embassy in Bogota.

The official said the identity of the kidnappers was still unknown. He confirmed that the four hostages -- three engineers and a translator -- are Chinese citizens.

President Juan Manuel Santos welcomed the news in a message on Twitter.

"I talked to the Chinese ambassador and want to celebrate the release of the four Chinese citizens. Kidnapping is not something that should be repeated again," the president wrote.

The head of Colombia's national police told reporters the hostages had been freed as a result of "a humanitarian operation orchestrated by the International Committee of the Red Cross and Chinese authorities."

The hostages were brought to a Red Cross office, Jose Roberto Leon Riano told reporters.

The Red Cross and the Chinese authorities "asked the Colombian government for humanitarian assistance, which it provided," Riano added, without giving details of the government's role.

Although he did not say who handed over the hostages on Wednesday, the police chief repeated government assertions that the FARC was behind the kidnapping.

"From the moment of the kidnapping, from intelligence information, it was known that the FARC were the ones with the Chinese citizens," he said.

The Red Cross said the hostages were brought to them by "unidentified men" in the town of San Vicente del Caguan.

"It's excellent news for the families of the freed people, after a long time of waiting and uncertainty," the head of the Red Cross in Colombia, Jordi Raich, said in a statement.

The hostages were working for the Emerald Energy oil company, a British-based subsidiary of China's Sinochem Group, when they were taken. Their Colombian driver was also seized, but released several hours later.

The Revolutionary Armed Forces of Colombia, Latin America's largest rebel group, has just begun peace talks with the government aimed at ending their decades-long conflict.

Earlier this year the FARC announced they would stop abducting civilians, whose ransoms had helped fund the group's activities. In early April, FARC rebels freed the last 10 policemen and soldiers they were holding.

But victims' associations in Colombia claim the rebels still hold a number of captives.