A senior Russian lawmaker said today that the resignation of Donald Trump's national security advisor, Michael Flynn, suggested Trump had been backed into a corner or that his administration had been 'infected' by anti-Russian feeling.

Flynn resigned late on Monday after revelations he had discussed US sanctions on Russia with the Russian ambassador to the United States before Trump took office and misled Vice President Mike Pence about the conversations.

'Either Trump has not gained the requisite independence and he is consequently being not unsuccessfully backed into a corner, or Russophobia has already infected the new administration also from top to bottom,' MP Konstantin Kosachev was cited as saying by the RIA Novosti news agency.

A US official told The Associated Press that Flynn was in frequent contact with Ambassador Sergey Kislyak on the day the Obama administration slapped sanctions on Russia for election-related hacking, as well as at other times during the transition.

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Former Army Lieutenant General Michael Flynn resigned from his position as Trump's National Security Advisor on Monday

It came after reports that Flynn was in frequent contact with Ambassador Sergey Kislyak (pictured above) on the day the Obama administration slapped sanctions on Russia in December

The Kremlin has confirmed that Flynn has been in contact with Kislyak but denied that they talked about lifting sanctions.

Kosachev, chairman of the foreign affairs committee of the upper chamber of the Russian parliament, said in a post on Facebook that firing a national security advisor for his contacts with Russia is 'not just paranoia but something even worse'.

Kosachev's counterpart in the lower chamber of the Russian parliament, Alexei Pushkov, said shortly after the announcement that 'it was not Flynn who was targeted but relations with Russia'.

Leonid Slutsky, head of the lower house of parliament's foreign affairs committee, suggested that Flynn was forced out of office.

'It's obvious that Flynn was forced to write the letter of resignation under a certain amount of pressure,' he was quoted as saying by the RIA news agency.

'The target was Russia-US relations, undermining confidence in the new US administration. We'll see how the situation develops further,' he said.

Meanwhile, Kremlin spokesman Dmitry Peskov said today that the resignation was an internal matter for the United States.

'We've said everything we want to say,' Peskov told reporters on a conference call.

Peskov has previously said that Flynn and the ambassador did not discuss lifting sanctions in their conversations.

He declined to elaborate on those earlier comments when asked on Tuesday.

The Russian Embassy to the United States, however, tweeted out a bizarre message hours before Flynn's resignation.

MP Konstantin Kosachev (left) said Flynn's resignation from national security advisor was a sign of 'not just paranoia but something even worse' in the White House. MP Alexei Pushkov (right) said shortly after the announcement that 'it was not Flynn who was targeted but relations with Russia'

Leonid Slutsky, head of the lower house of parliament's foreign affairs committee, suggested that Flynn was forced out of office

The Russian Embassy to the United States tweeted out a bizarre message hours before Flynn's resignation

'#Peskov: There have been no talks between #Russia and the #UnitedStates about the lifting of sanctions,' the Tweet said.

The message was accompanied by a photo of cheeseburgers and fries on a table with no one sitting around it.

There was no explanation for the photo, and Flynn was not mentioned.

In a link accompanying the message, Sputnik News reported that Peskov had told the media site: 'We have already said that there have been none', referring to discussions over sanctions between Russia and the United States.

It was reported last week that Flynn made explicit references to US sanctions on Russia in conversations with Kislyak.

One of the calls took place on December 29, the day Obama announced new penalties against Russia's top intelligence agencies over allegations they meddled in the US election process to help Trump win.

While it's not unusual for incoming administrations to have discussions with foreign governments before taking office, the repeated contacts just as the United States was pulling the trigger on sanctions suggests Trump's team might have helped shape Russia's response.

They also contradicted denials about such discussions of the sanctions by several Trump administration officials, including Vice President Mike Pence.

Flynn later backed off his adamant denials. On Friday, he said he 'no recollection' of discussing sanctions policy but 'can't be certain,' according to an official, who wasn't authorized to speak publicly on the matter and demanded anonymity.

MP Konstantin Kosachev suggested that Flynn's resignation showed that Trump was being 'backed into a corner', or that his administration had been 'infected' with 'Russophobia'

He apologized to Pence, who, apparently relying on Flynn's denials, vouched for him on television. In his resignation letter, Flynn said he held numerous calls with the Russian ambassador to the United States during the transition and gave 'incomplete information' about those discussions to Pence.

For days, Trump was publicly and unusually quiet on the matter. While his aides were declaring the president had confidence in Flynn, Trump privately told associates he was troubled by the situation, according to a person who spoke with him recently.

Reaction from the Democrats, however, was swift once news of Flynn's resignation was announced.

Rep. Adam Schiff (D-Calif.) said Flynn had always been a 'poor choice' as national security advisor, CBS reports.

He said it was not a job for someone who 'plays fast and loose with the truth'.

Schiff called for further investigation into any contact made between Russia and Donald Trump's campaign members.

Reps John Conyers Jr. (D-Mich.) and Elijah Cummings (D-Md.), respectively the ranking members of the Judiciary and Oversight committees issued a joint statement, according to The Hill.

'We were shocked and dismayed to learn this evening of reports that three weeks ago, U.S. law enforcement officials warned the White House Counsel that General Flynn had provided false information to the public about his communications with the Russian government,' they said.

'The reality is General Flynn was unfit to be the National Security Advisor, and should have been dismissed three weeks ago.'

'We need to know who else within the White House is a current and ongoing risk to our national security.'

Retired general Keith Kellogg will take over as acting National Security Advisor.