Robert Mueller, the special counsel probing Russia’s interference in the 2016 US presidential elections and its possible collusion with figures in the Donald Trump campaign, is reportedly investigating the financial dealings of the president’s senior adviser and son-in-law, Jared Kushner.

Citing “US sources familiar with the matter,” The Washington Post reported Thursday that the business dealings of additional former members of Trump’s team, including his campaign’s chairman, Paul Manafort, ousted security adviser Michael Flynn and ex-security adviser Carter Page, have also come under scrutiny.

“We do not know what this report refers to,” Kushner’s attorney Jamie Gorelick told The Post in an email. “It would be standard practice for the Special Counsel to examine financial records to look for anything related to ­Russia. Mr. Kushner previously volunteered to share with Congress what he knows about ­Russia-related matters. He will do the same if he is contacted in connection with any other inquiry.”

He is already at the center of the investigation into whether Trump officials colluded with Russia to sway the outcome of the presidential election. At issue are two meetings he had in December, during the Trump administration’s transition period: one with Sergey Kislyak, Russia’s ambassador to the United States, and the other with Sergey Gorkov, who runs a Russian state-owned bank and is close to Putin. The meetings were first reported in March.

It’s not entirely clear why Kushner met with Gorkov. The New York Times suggested it could have been part of Kushner’s attempt to create a direct line between the transition team and Putin. A Reuters report said the meeting could have concerned lifting US sanctions against Russia. But the bank said in a March statement that Gorkov met with Kushner in his capacity as a businessman.

Former FBI director Robert Mueller testifies on Capitol Hill in Washington, June 19, 2013, (AP Photo/J. Scott Applewhite)

Former FBI director Robert Mueller testifies on Capitol Hill in Washington, June 19, 2013, (AP Photo/J. Scott Applewhite)

In May, the Post reported that the meeting with Kislyak focused on setting up a back channel between the Trump transition team and Moscow. As opposed to official communications with other countries, a back channel aims to avoid oversight by the US government. Kushner reportedly proposed using Russian communications facilities for the back channel, but it was never established.

Kushner has been given a wide range of responsibilities in the Trump White House, from restructuring the federal government to achieving Middle East peace. He was one of the architects of Trump’s recent foreign trip, which especially in its visits to Saudi Arabia and Israel went smoothly and mostly gaffe-free.

On Wednesday, the Post reported that Mueller, the special counsel, who was appointed after the firing of FBI director James Comey, is now looking at whether Trump attempted to obstruct the investigation into possible collusion between his campaign and Moscow by leaning on Comey to drop the probe.

On Thursday, Trump denounced the report that he was being scrutinized for possible obstruction, calling it a “phony story.”

“They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story. Nice,” the president tweeted just before 4 a.m.

In a subsequent early-morning tweet, Trump called the investigation “the single greatest WITCH HUNT in American political history.”

Agencies contributed to this report.