Colombian President Juan Manuel Santos is vowing to have congress ratify a modified peace deal with the nation's largest rebel group rather than submit it again to voters, who rejected the first pact last month.

Speaking in Washington on Friday, Santos said implementing the accord in the shortest time possible would prevent a fragile cease-fire from falling apart. His comments came after two FARC rebels were killed in combat with security forces in a confusing incident now being investigated by United Nations-sponsored monitors.

Santos announced a week ago that FARC had agreed to modify the peace accord defeated in a referendum, but he had been cagey about how he intended to implement the deal.

Santos was addressing the Organization of American States after the hemispheric group endorsed the deal.