White House special advisor Jared Kushner, son-in-law of President Donald Trump, boasts an enormous portfolio of domestic and international responsibilities despite having no experience in politics before the 2016 campaign

Donald Trump, just back from his first international trip as US president, geared up to combat concerns Sunday over aides' ties to Russia including explosive reports that his son-in-law sought a secret communications line with Moscow.

The latest furor was stirred up after The Washington Post reported late Friday that Jared Kushner -- arguably Trump's closest White House aide, and husband to the president's eldest daughter Ivanka -- made a pre-inauguration proposal to the Russian ambassador to set up a secret, bug-proof link with the Kremlin.

Kushner, 36, even suggested using Russian diplomatic facilities in the United States to protect such a channel from monitoring, The Post said, quoting US officials briefed on intelligence reports.

The report, if confirmed, would raise new questions about the Trump team's relationship with the Russians, who US intelligence agencies say tried to sway the November election in Trump's favor.

News reports said the White House, reeling from the explosive developments in the long-running Russia saga, is creating a new rapid-fire communications unit to respond to the controversy, led by Kushner, senior presidential adviser Steve Bannon and White House Chief of Staff Reince Priebus.

Though Kushner has appeared "subdued," he does not plan to step aside as Trump's senior adviser or reduce his responsibilities, the New York Times reported, citing unnamed people close to him.

- 'Naive' or 'Sinister' -

After some delay, a senior Trump administration official en route back to Washington briefed reporters for almost 25 minutes, on matters from anti-terror cooperation to the administration's view that the summit had been a smashing success -- despite huge differences on climate change.

Trump plans to make an announcement within the week on his climate position, the official said.

But the said official did not address the Kushner reports Saturday.

Trump then returned to Washington Saturday night from his first overseas trip, to the Middle East and Europe. Accompanied by first lady Melania, Trump waved to reporters as he made his way into the White House but made no comment.

National Security Advisor H.R. McMaster refused to talk about the allegations. But he said that in general, "We have backchannel communication with a number of countries. What that allows you to do is communicate in a discrete manner."

"I would not be concerned about it," he added.

But a former head of the US National Security Agency harshly condemned Kushner's alleged effort to set up a secret communications line, saying if it is true, it would reveal a dangerous degree of ignorance or naivete.

"What manner of ignorance, chaos, hubris, suspicion, contempt would you have to have to think that doing this with the Russian ambassador was a good or appropriate idea?" Michael Hayden said on CNN.

He said he leaned toward "naivete" as an explanation, though he did not find it comforting.

Malcolm Nance, a retired naval officer and expert on terrorism and intelligence, said: "This is now sinister. There is no way this can be explained, from the intelligence perspective."

"That is indicative of espionage activity of an American citizen that is working in league with a hostile government," he told MSNBC.

The Washington Post said Kushner's secret communications proposal was made December 1 or 2 at Trump Tower in New York, according to intercepts of Russian communications that were reviewed by US officials.

Michael Flynn, who was Trump's national security adviser for just 24 days before being fired amid questions about meetings he held with the Russian ambassador, was also present, the newspaper reported.

The Post said the Russian ambassador to the United States, Sergei Kislyak, was surprised by the future White House aide's idea of a secret channel and passed it on to the Kremlin.

The New York Times said the channel was never established.

Trump returned to Washington to face a cascade of other worries related to the Russia probe in the coming days, including expected testimony by fired former FBI director James Comey before a Senate committee.

In another development, The New York Times reported Friday that Oleg Deripaska, a Russian once close to Trump's former campaign manager Paul Manafort, has offered to cooperate with congressional bodies probing alleged Russian election meddling.

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