GENEVA, August 6, 2008 (AFP) - Switzerland's foreign minister is to fly to Colombia Sunday, for a diplomatic trip overshadowed by Bogota's opening of an investigation into an alleged ransom paid for FARC-held Swiss hostages.

Micheline Calmy-Rey is due to meet Colombian President Alvaro Uribe and her counterpart Jaime Bermudez for talks on Monday, ostensibly to mark the 100th anniversary of the first Swiss-Colombian friendship treaty, an official told the Swiss ATS newsagency.

However, the authorites in Bogota have begun a inquiry into the role of Swiss mediator Jean-Pierre Gontard, suspected by Colombia of handing over a 500,000 dollar (323,000 euros) ransom to the Marxist guerilla group in return for the release of two Novartis employees in 2001.

Both Gontard and the Swiss foreign ministry deny the allegation.

Calmy-Rey in turn is expected to bring up the issue of the illicit use of the emblem of the International Committee of the Red Cross (ICRC) by the Colombian army during its rescue of French-Colombian hostage Ingrid Betancourt.

The symbol is protected by the Geneva Conventions and only allowed to be used by the ICRC itself.

Uribe admitted last month that one member of the rescue squad had worn the ICRC emblem, and apologised.

The jungle-based Armed Revolutionary Forces of Colombia (FARC) have fought a four-decade long struggle against the Colombian government, but are classed as a terrorist organisation by Washington and the European Union.

The Swiss minister is also scheduled to visit Medellin on Tuesday, where various Swiss-funded projects give humanitarian assistance and promote peace.

Calmy-Rey will then travel on to Brazil.