At the same time, several officials said that while Flynn held consultations with Kislyak in December, there was no evidence that he had made any promises to take actions to lift the sanctions after Trump's inauguration.
Flynn's contacts with the Russian ambassador reportedly started before the US presidential elections, and both of them confirmed that issue, though not specifying whether they discussed sanctions.
On Wednesday, Flynn denied allegations that he had discussed sanctions with Kislyak, however, the on very next day Flynn's spokesman said the security adviser was not sure that the issue of restrictive measures had never came.
The relations between Moscow and the West soured after Washington, Brussels and their allies accused Russia of fueling tensions in eastern Ukraine and introduced a series of sanctions against Russia as a punitive measure. Moscow has denied any involvement in the Ukrainian conflict and introduced countermeasures.
The latest round of sanctions was introduced in the end of December as retaliation for Russia's alleged meddling in US presidential elections, a claim that Moscow has also repeatedly denied.