Kremlin spokesman Dmitry Peskov said that it is premature to speak about extending the New START (Strategic Arms Reduction Treaty) until the discussion between the parties is held.

The news agency said Trump paused to ask aides what the treaty was, and then denounced it as favoring Russian Federation.

Spicer was asked the question in reference to a Reuters report which, citing unnamed sources, suggested that Trump had to ask an aide what the treaty was while on the call. It limits the deployment of land- and submarine-based missiles as well as nuclear bombers - the so-called nuclear triad that Trump was also unaware of - and it gives the former Cold War rivals until February 2018 to bring their deployed strategic nuclear warheads under 1,550, the lowest level in decades. In the letter to Trump, Ernst and the other senators asked him to "condemn" Russian aggression in Ukraine and "take...steps" to stop it.

Just before the call, the president also usually receives an oral "pre-briefing" from his national security adviser and top subject-matter aide, they said. "Trump's reported comments that New START is a "bad deal" and favored Russian Federation is simply wrong".

He also talked about his own popularity, two current and one former U.S. government officials claim.

While he couldn't remember it during his phone call with Putin, Trump had actually previously criticized the deal during a campaign debate where he erroneously referred to it as the "START-Up" treaty (which maybe explains his confusion).

The Russian leader hailed Slovenia, where Trump's wife Melania was born and grew up, as an "excellent" venue for possible talks with Trump.

Despite promises to engage more with Russia, Trump has expressed the need to strengthen the US nuclear arsenal. Putin wanted an extension, and Trump apparently drew a blank.

The Reuters exclusive was based on two sources who were briefed by people who read the notes taken, along with another person briefed on the January 28 call. Segments of transcripts of Trump's calls with the leaders of Mexico and Australia revealed conversations that were contentious in tone, although the Trump administration insisted that both calls went well and were friendly in nature.

"I would say they had a very productive call", he told reporters.

The White House described the conversation as a "significant start to improving the relationship between the United States and Russian Federation that is in need of fix".

A bipartisan group of senators on Wednesday introduced legislation that would boost congressional oversight before Trump can lift sanctions on Russian Federation for its intervention in Ukraine or USA election meddling.