Colombian rebels say they are putting off plans to free six hostages held for more than 10 years because of what they say is military activity in the area.

The Revolutionary Armed Forces of Colombia, or FARC, said Wednesday it will make another attempt to free its captives as soon as what it calls the president's "insanity" abates.

Colombian President Juan Manuel Santos says nobody knows where the hostages are being held. He appealed to the rebels to stop what he says are tricks and deceptions, and free the hostages now.

FARC is Colombia's largest rebel group. Its fight with the government has killed tens of thousands of people over the past 50 years.

The government says FARC murdered four other hostages in November when troops attempted a rescue.

Some information for this report was provided by AFP and Reuters.