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, according to Reuters.
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. It referred Reuters to the official White House account issued after the Jan. 28 call, which did not mention the discussion about New START.
Read alsoCNN: Senators seek Hill veto power over Trump on RussiaIt 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.
Read alsoKremlin: East Ukraine unlikely to be part of deal with TrumpDuring a debate in the 2016 presidential election, Trump said Russia had "outsmarted" the United States with the treaty, which he called "START-Up." He asserted incorrectly then that it had allowed Russia to continue to produce nuclear warheads while the United States could not, Reuters reports.