Washington( CNN) US investigators wiretapped former Trump campaign chairman Paul Manafort under secret court orders before and after the election, sources tell CNN, an extraordinary step involving a high-ranking campaign officer now at the center of the Russia meddling probe.

Some of the intelligence collected includes communications that sparked fears among examiners that Manafort had encouraged the Russians to help with the campaign, according to three sources familiar with the investigation. Two of these sources, nonetheless, cautioned that the evidence presented is not conclusive.

Special counsel Robert Mueller’s team, which is leading the inquiry into Russia’s involvement in the election, has been provided details of these communications.