The U.S. State Department is urging Colombia's largest leftist rebel group, the FARC, to immediately release all hostages in its custody, saying the U.S. holds the guerrillas responsible for the captives' health and well-being.

State Department spokesman Sean McCormack made the remark Wednesday in a statement that coincided with the fifth anniversary of the FARC's kidnapping of three American defense contractors, Marc Gonsalves, Thomas Howes and Keith Stansell.

McCormack said the contractors were on a joint U.S.-Colombia anti-drug reconnaissance mission when their aircraft made an emergency landing due to mechanical failure. FARC members patrolling the area captured them and killed two crew members.

The spokesman said the United States fully supports the Colombian government in its efforts to achieve the safe recovery of all hostages, some of whom have been held for 10 years.

Earlier this month, tens of thousands of Colombians marched to demand that the FARC stop kidnapping people and release its captives. FARC hostages include French-Colombian politician Ingrid Betancourt, who was kidnapped six years ago, and at least 40 other high-profile captives. The FARC holds about 750 hostages in jungle hideouts.

The U.S., European Union and Colombia have classified the FARC as a terrorist organization.