Updated

U.S. counterintelligence agents have investigated communications that President Donald Trump’s national security adviser had with Russian officials, according to people familiar with the matter.

Michael Flynn is the first person inside the White House under Mr. Trump whose communications are known to have faced scrutiny as part of investigations by the Federal Bureau of Investigation, Central Intelligence Agency, National Security Agency and Treasury Department to determine the extent of Russian government contacts with people close to Mr. Trump.

A key issue in the investigation is a series of telephone calls Mr. Flynn made to Sergey Kislyak, the Russian ambassador to the U.S., on Dec. 29. That day, the Obama administration announced sanctions and other measures against Russia in retaliation for its alleged use of cyberattacks to interfere with the 2016 U.S. election. U.S. intelligence officials have said Russian President Vladimir Putin ordered the hacks on Democratic Party officials to try to harm Hillary Clinton’s presidential bid

In a statement Sunday night, White House spokeswoman Sarah Sanders said: “We have absolutely no knowledge of any investigation or even a basis for such an investigation.”

Earlier this month, Sean Spicer, then spokesman for the Trump transition team and now White House press secretary, said the contacts between Messrs. Flynn and Kislyak dealt with the logistics of arranging a conversation between Mr. Trump and Russia’s leader.

“That was it,” Mr. Spicer said, “plain and simple.”

U.S. officials have collected information showing repeated contacts between Messrs. Flynn and Kislyak, these people said. It is common for American officials’ conversations with foreign officials to surface in NSA intercepts, because the U.S. conducts wide-ranging surveillance on foreign officials. American names also may surface in descriptions of conversations shared among officials of foreign governments.

The Senate Intelligence Committee is also looking into any possible collusion between Russia and people linked to Mr. Trump, top senators have said. That is part of the committee’s broader probe into Russian election interference. Counterintelligence probes seldom lead to public accusations or criminal charges.

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