House Democratic leader Nancy Pelosi accused Sessions of “lying under oath” and demanded he resign.
Sessions had more than 25 conversations with foreign ambassadors last year in his role as a US senator and senior member of the Armed Services Committee.
And he had two separate interactions with the Russian ambassador, Sergey Kislyak, the Justice Department confirmed.
In a statement on Wednesday, Sessions said: “I never met with any Russian officials to discuss issues of the campaign. I have no idea what this allegation is about.
“It is false.”
The claims are the latest in a string of similar revelations to hit the fledgling administration, still only a little over a month old.
Dr Brian Klaas, fellow in comparative politics at the London School of Economics, told The Huffington Post UK: “Never has an administration been embroiled in scandal so early in modern presidential history.
“To have a National Security Advisor resign in the first month and allegations of the Attorney General lying under oath in the second month is not the ‘fine-tuned machine’ that Trump boasted about.”
Sessions is in a particularly delicate situation as his role as Attorney General means he is overseeing a federal investigation into Russian interference in the presidential election.
“Politically, this makes any internal Department of Justice investigation impossible. Sessions cannot investigate himself,” added Dr Klaas.
“As a result, this will renew calls for a Special Prosecutor to investigate whether there was inappropriate or illegal contact between Trump, or Trump’s campaign surrogates, and the Russian government.
“This will also renew calls for Trump to release his tax returns―as every presidential candidate has done since the Nixon scandals in the 1970s. Americans will want to see evidence that Trump himself does not have business links or major debts to Russia.”
At Sessions’ confirmation hearing in January, Sen. Al Franken of Minnesota asked Sessions what he would do if there were evidence that anyone from the Trump campaign had been in touch with the Russian government during the campaign.
Sessions replied he was “unaware of those activities”.
He added: “I have been called a surrogate at a time or two in that campaign and I didn’t have, did not have communications with the Russians, and I’m unable to comment on it.”
A Justice Department spokeswoman said that response was not misleading.
Sessions and Flynn join four other Trump affiliates accused of having undisclosed contact with Russian officials in 2016.
Former campaign manager, Paul Manafort, was identified by US intelligence officials though he said he had “never knowingly spoken to Russian intelligence officers”.
He resigned from his position in August after being implicated in a scandal involving payments from the political party of Viktor Yanukovych, former president of Ukraine and Vladimir Putin ally.
Trump’s confidante and election campaign advisor, Roger Stone, is also under the microscope and has said he would welcome an investigation.
Trump’s personal lawyer, Michael Cohen, reportedly hand-delivered a secret “peace plan” to resolve the conflict between Russia and Ukraine and in turn lift American sanctions.
Former foreign policy adviser, Carter Page, is alleged to have met with Russian internal affairs official, Igor Divyekin, to discuss “kompromat” (compromising material) on Trump.
Stone, Flynn, Manafort, and Page were all named by The New York Times as having been under FBI investigation over the links.
Revelations of Sessions’ contacts, first reported by The Washington Post, came amid a disclosure by three administration officials that White House lawyers have instructed aides to Trump to preserve materials that could be connected to Russian meddling in the American political process.
The officials who confirmed that staffers were instructed to comply with preservation-of-materials directions did so on condition of anonymity because they were not authorised to publicly disclose the memo from White House counsel Don McGahn, the Associated Press reported.
But observers have said there’s now a more urgent pressure on Trump following the revelations.
“Whether he will cooperate with the investigations or continue to call them ‘fake news’ is anyone’s guess,” Dr Klass told HuffPost UK. “But Republicans are being put in a position where it is becoming politically impossible to ignore this.”