(Adds background and United Nations quote in paragraph nine)

By Hugh Bronstein

BOGOTA, July 25 (Reuters) - Colombian rebels are planting more and more landmines in rural areas where children and farmers have their legs torn off and eyes ripped out every time they step on one, a rights group said on Wednesday.

Civilian casualties from the explosive devices rose to 314 in 2006 from 66 in 2000, says a report from New York-based Human Rights Watch.

Colombia's biggest guerrilla army, the FARC, is increasing its use of mines that are often detonated by children walking to school or farmers working their fields, says the report based on victim interviews and government figures.

"Guerrillas' frequent use of antipersonnel landmines, improvised from cheap, readily available materials, leaves hundreds of civilians maimed, blind, deaf or dead every year," the report says.

Of last year's civilian casualties, 66 were children.

The report cites cases such as that of a 10-year-old girl blinded by a mine explosion and a 9-year-old boy who said he feels "incomplete" after having one of his hands blown off.

From 1990 to 2000 Colombian landmine casualty reports, including military victims, never exceeded 148 per year. In 2001 the reports started climbing and stood at 1,107 in 2006.

Colombia says it had the highest number of landmine victims in the world in 2005 and 2006. Complete figures are hard to estimate as many victims do not register with authorities.

Last week two boys from a western Colombian indigenous group were killed by a mine as they ran toward their father who lay dying in a field after stepping on one himself, said U.N. agency UNICEF, which calls landmines a "persistent and insidious" threat to children in this Andean country.

The FARC and the smaller rebel group ELN started their communist insurgencies in the 1960s. In the 1980s cattle ranchers and cocaine lords formed paramilitary militias to defend against rebel kidnappings and land grabs.

By the late 1990s the guerrillas and their paramilitary enemies, both labeled terrorists by Washington, had directly entered Colombia's multibillion-dollar cocaine trade.

Colombia and most other governments have banned the use of mines. But the FARC and ELN use them to keep soldiers and police away from camps used to hold kidnap victims, coca crops used to make cocaine and other strategic positions.

Human Rights Watch called on both to stop using indiscriminate weapons such as landmines and bombs made from cooking gas cylinders, which are fired like missiles but cannot be aimed accurately.

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