MOSCOW (AFP, REUTERS) - The Kremlin on Tuesday (Feb 14) insisted that the resignation of Donald Trump's security adviser Michael Flynn over contacts with the Russian government was Washington's internal affair.

The White House late Monday said Trump had accepted Flynn's resignation amid allegations the retired three-star general discussed US sanctions strategy with Russia's ambassador Sergey Kislyak before taking office.

"This is the internal business of the Americans, it is the internal business of President Trump's administration. This is not our business," Kremlin spokesman Dmitry Peskov told journalists.

Flynn admitted that he "inadvertently briefed" the now Vice President Mike Pence with "incomplete information" about his calls with Kislyak.

Pence had publicly defended Flynn, saying he did not discuss sanctions, putting his own credibility into question.

US media reported Monday that the Justice Department had warned the White House that Flynn had misled senior administration officials about the contents of his talks with Kislyak, and that it could make him vulnerable to Russian blackmail.

The Kremlin has previously denied that Flynn and Kislyak discussed the lifting of US sanctions.

The resignation of the top aide is a first stunning departure from the president's inner circle less than a month after his inauguration.

Flynn - who has previously met President Vladimir Putin - was a vocal supporter of a softer policy on Russia after ties plunged over Moscow's meddling in Ukraine and allegations of interference in the US election.

Meanwhile, senior Russian lawmakers said on Tuesday the resignation of US President Donald Trump's national security adviser showed that efforts were being made to undermine Russian-US relations.

"It's obvious that Flynn was forced to write the letter of resignation under a certain amount of pressure," Leonid Slutsky, head of the lower house of parliament's foreign affairs committee, was quoted as saying by the RIA news agency.

Fellow lawmaker Konstantin Kosachev, who leads the upper house of parliament's international affairs committee, said the resignation could be a sign of growing anti-Russian feeling in the White House.

"Either Trump has not gained the requisite independence and he is gradually being (not unsuccessfully) backed into a corner, or Russophobia has already infected the new administration also from top to bottom," Kosachev said on social media.

US-Russia relations deteriorated to their worst level since the Cold War under the Obama administration, which slapped economic sanctions on Russia for its annexation of Crimea in 2014 and its involvement in Ukraine's separatist conflict.