The FBI began its probe, which also is examining whether there was collusion between the Trump campaign and Moscow, in July
The FBI investigated Trump campaign advisor Carter Page last year over worries he could have been working for Russia, the Washington Post reported Tuesday.
In the first confirmation that the government conducted surveillance on President Donald Trump's team, the Federal Bureau of Investigation obtained a rare warrant to monitor the Page's communications from the top secret Foreign Intelligence Surveillance Court, the Post said.
The so-called FISA warrant was issued after the FBI told the court that there was probable cause to believe the former Moscow-based banker was working for Russia.
FISA warrants are almost never made public, and the Post cited unnamed law enforcement and other officials in its report. The FBI did not respond to requests to comment on the report.
The warrant was granted as the FBI conducted a counterintelligence investigation into Russian interference in the election, an operation US intelligence later concluded was ultimately designed to help President Donald Trump to victory.
The FBI began its probe, which also is examining whether there was collusion between the Trump campaign and Moscow, in July.
Trump has repeatedly called the Russian interference story "fake news" while alleging, without offering evidence, that the previous administration of president Barack Obama spied on him and his campaign.
In March 2016 Trump named Page as one of his small team of foreign policy advisors, and he attended the Republican convention in July, where he and others met with Russian Ambassador Sergey Kislyak.
But months later Page was disavowed by the campaign, apparently in part because of the attention drawn by his trips to Moscow, which he said were private business.
His name surfaced in a dossier or reports on links between the Trump operation and Russia complied by former British spy Christopher Steele.
Page told the Post he had "nothing to hide."
"This confirms all of my suspicions about unjustified, politically motivated government surveillance," Page said.
In March he told Fox News that he did not help the Russians in their efforts to influence the campaign.
"I did nothing that could even possibly be viewed as helping them in any way," he said.
Meanwhile CNN reported Tuesday that recent intelligence reports brought to light by a Republican Congressman Devin Nunes did not show, as Nunes alleged, that the Obama administration combed intelligence intercepts to find information about Trump and his team.
CNN said bother Republican and Democratic sources said the reports showed Obama national security advisor Susan Rice had handled the intelligence in "normal and appropriate" ways.
Nunes was forced to step aside as chair of the House Intelligence Committee's investigation of russian election interference due to his own mishandling of those reports.