U.S. Secretary of State Marco Rubio on Saturday threatened bounties on the heads of Afghanistan's Taliban leaders, sharply escalating the tone as he said more Americans may be detained in the country than previously thought.

A year ago, a prisoner exchange between the United States and the Taliban brought relief to families waiting for the return of their loved ones. The deal was seen as a rare moment of cooperation between Washington and the Afghan government.

Secretary of State Marco Rubio warned about a “very big bounty” on top Taliban leaders if they are holding more American hostages than was reported.