Story highlights The FBI and Justice Department obtained a Foreign Intelligence Surveillance Act warrant last summer

Page called the FISA warrants "unjustified" in a statement to CNN

Washington (CNN) The FBI obtained a warrant to monitor President Donald Trump's former campaign adviser, Carter Page, last summer on suspicions he knowingly engaged in clandestine intelligence activities on behalf of Moscow, The Washington Post is reporting.

The FBI and Justice Department obtained a Foreign Intelligence Surveillance Act warrant to monitor the communications of Page, who has called himself a junior member of Trump's foreign policy advisory team, as part of their investigation into possible ties between Trump's campaign and Russia, the newspaper says, citing unnamed law enforcement and other US officials.

The FBI and Justice Department obtained the warrant after convincing a FISA judge there was probable cause to believe Page was acting as an agent of a foreign government (Russia), the report says. The warrant presents the strongest information to date that the FBI had reason to believe a Trump adviser was in touch with Moscow and met with foreign operatives during Trump's presidential campaign.

FBI Director James Comey has acknowledged that an investigation was opened last year into Russia's efforts to influence the election and the question of whether the Trump campaign coordinated with the Kremlin. But Comey stopped short of naming anyone working for the campaign who may have been involved.

CNN is working to confirm The Washington Post's story.

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