By Hugh Bronstein

BOGOTA, March 28 (Reuters) - Leftist Colombian rebels on Wednesday released four of nine geologists who were kidnapped two weeks ago while prospecting for gold in the western jungle province of Choco, the Red Cross said.

"They only turned four people over to us. We do not know about the other five," a Red Cross spokesman told Reuters. "We remain available to support the liberation of the remaining hostages."

The Revolutionary Armed Forces of Colombia, or FARC, customarily hands hostages over to the Red Cross when liberating them. The 17,000-member rebel army is fighting a 40-year-old insurgency funded by kidnapping for ransom and the Andean country's multibillion-dollar cocaine trade.

On March 13, the FARC kidnapped the prospectors at gunpoint and marched them into the jungle near the provincial capital, Quibdo.

The prospectors work for a company called Logistical Services, based in Medellin, where the four victims were reunited with their families after their midday release.

Other rebel hostages include Ingrid Betancourt, a French-Colombian citizen kidnapped during her 2002 presidential campaign and three American defense contractors kidnapped in 2003 while on a mission to locate crops used to make cocaine.

Choco is sandwiched between Panama to the north, a common destination for smugglers, and Valle del Cauca province to the south, home to Colombia's toughest drug cartel.

Colombians have been riveted by a television news series this week about children dying of malnutrition in Choco, where entire villages are often displaced by the FARC and other groups battling over lucrative cocaine-producing land.

Most people in the province are descended from African slaves brought by the Spanish to work in local gold mines.

Thousands are killed in Colombia's war every year. But crime is down under President Alvaro Uribe, who won a second term in 2006 based on his popular U.S.-backed crackdown on the FARC, which is branded a terrorist organization by Washington.

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