Special counsel Robert Mueller is casting a wide net in his Russia investigation — grilling Russian oligarchs about President Trump’s campaign when they traveled into the US, a new report said Wednesday.

Mueller’s team even intercepted one oligarch and searched his electronic devices when his private jet landed at a New York-area airport, CNN reported, citing sources familiar with the probe.

Another Russian big shot was stopped during a recent trip to the US, although it was unclear if he was searched, the network reported.

Mueller’s investigators also made a voluntary document and interview request to a third Russian oligarch who had not traveled to the US recently.

The investigators want to know whether wealthy Russians illegally funneled cash into Trump’s presidential campaign and inauguration.

The special counsel is investigating Russian meddling in the 2016 election and possible collusion with the Trump campaign.

The president has adamantly denied collusion, has attacked Mueller on Twitter and called his probe “a hoax,” “fake news” and a “witch hunt.”

Foreign nationals are banned from giving money to US political campaigns.

One area under scrutiny, CNN reported, was investments the unidentified Russians made in companies or think tanks that have PACs that gave money to Trump.

Another theory being explored is whether rich Russians used straw donors — Americans with citizenship — to funnel cash to the campaign and inauguration fund.

“Prosecutors and investigators like the element of surprise when you can get more instinctive (and often truthful) responses,” Daniel Goldman, a former federal prosecutor, told the network in a text.