Rex Tillerson's comments came in a written response to questions that members of the Senate Foreign Relations Committee sent to him as part of the confirmation process.
As the staunchest US ally in Latin America, Colombia has received billions of dollars in US aid over the past two decades to combat drug trafficking and leftist rebels who fund their insurgency from it.
The Obama administration was a key backer of President Juan Manuel Santos' efforts to end the half-century conflict by appointing a special envoy to the talks and promising USD 450 million more in US aid to make sure the peace agreement signed last year holds.
They were confirmed by a Senate aide who requested anonymity because he was not authorised to share them with journalists.
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Tillerson said he would "make every effort" at continuing the partnership. But he said he plans to hold Colombia to its commitment to rein in drug production amid a surge in cocaine flowing from the country that many critics attribute to Santos' decision in 2015 to suspend US-backed aerial fumigation of illegal coca crops.
Chris Sabatini, editor of Latin America Goes Global, said Tillerson's seeming doubts about the peace deal reflect a growing skepticism within Republican circles that have been stoked by conservative former President Alvaro Uribe.
Uribe led the campaign that defeated the original peace deal in a referendum only to see Santos go ahead and ratify a revised accord a few weeks later.
"Across-the-aisle consensus on Plan Colombia helped Colombia dramatically reduce crime and violence, assisted the state in recovering its territorial integrity, led to the disarming of paramilitaries and beat back the guerrillas to the negotiating table," Sabatini said.
On the region's other hot spots Tillerson's views seems much more aligned with current policy.
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