Former U.S. President Bill Clinton offered some rare words of praise for Vladimir Putin on Wednesday, describing the Russian president as "very smart," "brutally blunt" and true to his word.

"Mr. Putin … he's very smart," Clinton said in an interview with CNN talk show host Piers Morgan. "And, remarkably, we had a good, blunt relationship." Asked to describe just how blunt that relationship was, Clinton replied, "Brutally blunt," indicating he preferred this level of frankness in private conversations.

Putin took over as acting Russian president on Jan. 1, 2000, following the surprise New Year's Eve resignation of the late Russian leader Boris Yelstin, and was formally elected for his first term two months later. Clinton, who left office in January 2001, worked with him as head of state for a year.

Asked if Putin ever reneged on a promise, Clinton was categorical: "He did not."

"He kept his word on all the deals we made," Clinton said.

Broadcast of the interview came as some U.S. officials publicly question whether the United States should trust Putin — both the man and his administration — enough to invest fully in a new Russia-U.S. push to destroy chemical weapons in Syria and sponsor negotiations to end the two-year conflict there.

The joint effort staved off what appeared to be imminent U.S. military action in Syria earlier this month, but many U.S. politicians have voiced skepticism on whether it will bear fruit.

"We do have to believe it" will help, Clinton said of the latest Russian-U.S. effort. "We just have to see what happens and make the most of what happens," he said, adding that "it would be a terrible mistake" not to explore viable opportunities for resolving the Syrian crisis peacefully.