Colombia's government and leftist FARC rebels were set to kick off peace talks in Norway on Thursday in what a Bogota official called a "respectful and cordial" atmosphere.

Oslo and later Havana are hosting the talks that seek to end Latin America's oldest conflict, which has claimed hundreds of thousands of lives in the past 50 years.

The government and rebel sides were to hold a press conference at 3:00 pm (1300 GMT) in a hotel in Hurdal, a small town north of Oslo, to officially launch the negotiations.

A Norwegian government official told AFP that for now no other public events were planned.

After their start in Norway, the talks will move to the Cuban capital.

The United States, a long-time ally of the Colombian government in its fight against drug trafficking, a major source of funding for the rebels, Wednesday voiced "full support" for the peace process.

The Americans are not involved but are being updated regularly, said Victoria Nuland, a spokeswoman for the State Department.

A Colombian official, asked about preparatory meetings on the negotiations' logistics, told AFP the talks had been "respectful and cordial".

The Colombian government has voiced cautious optimism about a deal.

"We do not want to create false expectations, but we do believe there are structural elements that allow us to harbour hope that we will see good news for Colombia," chief government negotiator Humberto de la Calle told AFP before leaving Bogota.

Preparations for the Oslo talks have been cloaked in secrecy, with few details seeping out from either the delegations or host Norway about the fourth official attempt to resolve Colombia's insurgency.

Latin America's largest rebel group, founded in 1964 and with 9,200 armed fighters now, FARC -- the Revolutionary Armed Forces of Colombia -- may be ready for a truce after a long string of setbacks.

In recent years, it has suffered the capture and killings of some of its top leaders, and the depletion of its ranks to half what they were at their peak in the 1990s.

Topics for discussion including the rebels' future role in political life, a definitive end of hostilities, fighting the illegal drug trade and boosting rural development.

Colombian President Juan Manuel Santos has rejected a ceasefire before a final agreement is reached, but the issue is expected to be raised by FARC.

The rebels sparked last-minute controversy by revealing that Dutch national Tanja Nijmeijer, a FARC member for the past decade, would be among the delegates at the peace talks in Havana.

Allowing the rebels' only known European recruit in the delegation is a controversial move, since it is seen by the government side as an attempt by FARC to curry favour in Europe and bolster its international image.

Nijmeijer, 34, first travelled to Colombia to study philology and teach English. Affected by abuses and inequality she witnessed, she joined FARC in 2002 and has since risen to the senior ranks.

FARC is considered a terrorist organisation by the United States and the European Union.

Former Colombian president Alvaro Uribe said Wednesday he was "concerned" about the talks, saying he didn't understand why a country would "negotiate with terrorists".

Issues such as health care, education, land reform and drug trafficking should not be negotiated with terrorists, he said in an interview with Spanish daily ABC.

"The government is trying to strike a deal with FARC at the price of security, and engages in dialogue while security is deteriorating, without requiring FARC to end its criminal activities."