US officials interviewed hundreds of employees this week at the US embassy in Ukraine regarding the alleged surveillance of Marie Yovanovitch, the former American ambassador there, by associates of Rudy Giuliani, according to reports.

The surprise detective work was performed by officers from the State Department’s Diplomatic Security Services over two days, BuzzFeed News reported Saturday.

It came less than a week after Secretary of State Mike Pompeo promised to cooperate with Ukrainian authorities in an investigation stemming from documents released by Lev Parnas, a Giuliani associate who has been charged with campaign finance violations.

A string of text messages between Parnas and Robert Hyde, a Trump supporter and current congressional candidate from Connecticut, suggested that Hyde had Yovanovitch — a Trump critic — under electronic and physical surveillance.

Both Parnas and Hyde have denied the allegation, dismissing the messages as idle boasts.

Meanwhile, Pompeo — who is scheduled to visit Ukraine next week — came under fire Saturday for exploding at an NPR reporter who grilled him about his support for Yovanovitch, who was fired by Trump last year.

Pompeo issued a defensive statement calling it “shameful” for NPR’s Mary Louise Kelly to have publicized what he claimed to have been an off-the-record conversation — which Kelly denied.

But a group of five Senate Democrats sent Pompeo a letter calling his “insulting and contemptuous” behavior “beneath the office of the Secretary of State.”