US intelligence officials have reportedly warned their counterparts in Israel to "be careful" when sharing classified information with the upcoming Trump administration amid concerns that sensitive data may be leaked to Russia, and onwards to its ally Iran.

According to investigative journalist Ronen Bergman, American agents said during a recent "closed forum" that until it is clear Trump is not "being extorted by the Kremlin" Israeli operatives should "avoid revealing sensitive sources to administration officials" or the White House.

Writing in Israel-based publication Ynetnews, Bergman said his sources' fears of intelligence leakages spiked following recent chatter about ties between President-elect Trump and Moscow, whose agents are believed to have links with Tehran.

He did not reveal the names of those in attendance, nor its date, but said US officials claimed during the meeting that Russian president Vladimir Putin has gathered "leverages of pressure" over Trump.

They also reportedly voiced "despair" over his election win because of his critical stance on US intelligence agencies.

Lastly, Bergman said he was told US spies at the National Security Agency (NSA) had obtained "highly credible information" that Russia was responsible for hacking into the Democratic National Committee (DNC) and handing the information to WikiLeaks.

This week (10 January) a CNN splash claimed the Russian government had collected a plethora of "personal and financial information" on President-elect Trump for the purpose of blackmail – a tactic known as kompromat in Russia. Buzzfeed later released the unverified documents in full.

This leaked file, purportedly authored by former MI6 agent Christopher Steele, accused Trump of having a long relationship with officials in Russia and being part of an "extensive conspiracy" with the Kremlin. It also made lurid references to "perverted sexual acts" involving the president-elect.

In response to the reports, Trump branded them "fake news" and "a total witch hunt." He later tweeted: "Intelligence agencies should never have allowed this fake news to 'leak' into the public. One last shot at me. Are we living in Nazi Germany?"

A spokesman for Russian president Vladimir Putin dismissed the unverified report's allegations. "The Kremlin has no compromising dossier on Trump, such information isn't consistent with reality and is nothing but an absolute fantasy," said Dmitri Peskov, the Associated Press (AP) reported.