In his first call as president with Russian leader Vladimir Putin, Donald Trump denounced a treaty that caps U.S. and Russian deployment of nuclear warheads as a bad deal for the United States, according to two U.S. officials and one former U.S. official with knowledge of the call.

When Putin raised the possibility of extending the 2010 treaty, known as New START, Trump paused to ask his aides in an aside what the treaty was, these sources said.

Trump then told Putin the treaty was one of several bad deals negotiated by the Obama administration, saying that New START favored Russia. Trump also talked about his own popularity, the sources said.

The White House declined to comment on the details of the call. White House spokesman Sean Spicer said Trump knew what the New START treaty is but had turned to his aides for an opinion during the call with Putin. He said the notes from the call would not have conveyed that.

"I would say they had a very productive call," Spicer told reporters. He added, "It wasn't like he didn't know what was being said. He wanted an opinion on something."

It has not been previously reported that Trump had conveyed his doubt about New START to Putin in the hour-long call.

New START gives both countries until February 2018 to reduce their deployed strategic nuclear warheads to no more than 1,550, the lowest level in decades. It also limits deployed land- and submarine-based missiles and nuclear-capable bombers.