* High-profile journalist escaped assassination attempt
* Hit man in Colombia's capital, government agency says
By Helen Murphy
BOGOTA, May 14 (Reuters) - Colombia on Tuesday warned of a plot by an organized crime group to kill several high-profile journalists, just weeks after an assassination attempt on an investigative reporter boosted concerns over threats to a free press in the violence-plagued Andean nation.
Journalists and investigators have long been the target of attacks and threats in Colombia, allegedly carried out by corrupt politicians, drug lords, Marxist rebels, and right-wing paramilitary leaders to silence coverage that may damage their interests.
A hit man has entered the Colombian capital to kill columnist Leon Valencia, analyst Ariel Avila and reporter Gonzalo Guillen, according to Andres Villamizar, head of a government-run agency to protect high-profile targets.
"We won't allow these plans to be carried out," Villamizar said early Tuesday from his Twitter account, pledging to step up security.
Even though a U.S.-backed military offensive has improved security over the last decade, the threats throw a spotlight once more on the dangers for reporters covering corruption and criminal gangs in Colombia, just when the government is seeking a peace accord with the biggest rebel group, the FARC.
The threat likely stems from an investigation into links between paramilitary groups and politicians during last year's municipal elections, Valencia, a former ELN rebel and columnist for respected Semana magazine, told Reuters. The hit man is thought to have traveled from the northern Cesar province.
"No doubt we're afraid because the people involved are very powerful and have no limits," the former member of the National Liberation Army said. "We will continue investigating, nothing will stop us."
Paramilitary groups continue to operate across Colombia even after former President Alvaro Uribe negotiated their demobilization in 2008 and many handed in their weapons in exchange for soft jail sentences. Thousands have morphed into new drug-funded crime gangs and continue to kill and threaten if their operations are at risk.
It was not immediately clear why Guillen would be targeted alongside Valencia and Avila.
Colombia has been rattled by a five-decade war against various insurgent groups - including the Revolutionary Armed Forces of Colombia, or FARC, and paramilitary forces - that has killed more than 100,000 people and forced millions to flee their homes.
Some analysts believe the threat against the press never receded. Journalists simply watered down their coverage and engaged in self censorship to remain under the assassin's radar.
The new generation of criminal gangs is now fighting with the FARC and paramilitary groups for control of drug-smuggling routes and illegal activities, while journalists, union workers and residents are often caught in the middle.
The latest threat comes on the heels of an assassination attempt two weeks ago on Ricardo Calderon, an investigative journalist who narrowly survived an ambush that riddled his car with bullets as he returned to Bogota after reporting on irregularities in a military prison for Semana magazine.
Last week, eight journalists were given 24 hours to leave the city of Valledupar, in Cesar province, as they reported on government attempts to return stolen land to war victims. Leaflets authored by a little-known group, the Anti-land Restitution Army, declared the reporters collaborators and hence targets for death.
Paramilitary groups and FARC rebels have seized millions of acres (hectares) of land from residents in Colombia, either under threat of death or as they fled the fighting. The government is seeking to return the land, but already many activists have been murdered for trying to reclaim their property.
All the reporters and analysts threatened have worked on some of the most damning stories, including corruption in northern La Guajira province, the government's intelligence agency wire tapping opponents, and right-wing paramilitary involvement in the nation's Congress. (Additional reporting by Luis Jaime Acosta in Bogota; Editing by Vicki Allen)