Since confirming last week that Soleimani had been killed by a U.S. airstrike in Baghdad, President Donald Trump's administration has claimed that the bold move was taken in part because Soleimani was "actively developing plans to attack American diplomats and service members in Iraq and throughout the region."

"There was no doubt that there were a series of imminent attacks that were being plotted by Qasem Soleimani. And we don't know precisely when and we don't know precisely where, but it was real," Pompeo said in an interview that aired Thursday night on Fox News.

The U.S. did not know exactly when slain Iranian military leader Qasem Soleimani had planned to attack Americans, Secretary of State Mike Pompeo said while maintaining the Trump administration's line that such strikes were about to happen.

Neither the White House nor the Pentagon immediately responded to CNBC's requests for comment on Pompeo's remarks.

The administration has been circumspect about what those plans actually entailed and when they were expected to be carried out. Some members of Congress, including a few Republicans, have complained that the administration's classified briefing on Capitol Hill was insufficient.

"Why last Friday? What had happened that provoked this rather startling strike at this particular moment in time?" Sen. Angus King, I-Maine, asked on CNBC's "Squawk Box" on Thursday.

Almost all members of Congress have agreed that Soleimani, who has been blamed for the deaths of hundreds of Americans, had posed a threat to the U.S.

Pompeo told Fox it's "most unfortunate" that "a number of people are using this as a political ax to grind."

Despite the lack of specifics, Trump has made a series of claims, without providing evidence about what Soleimani had planned.

At a Thursday night rally in Toledo, Ohio, Trump told an auditorium packed with supporters that "Soleimani was actively planning new attacks, and he was looking very seriously at our embassies, and not just the embassy in Baghdad."

Fox opinion host Laura Ingraham asked Pompeo about that claim.

"It was his forces that penetrated our embassy just a handful of days before that," Pompeo responded. "I don't think there's any doubt that Soleimani had intentions not only against our forces, our diplomats in Iraq, but in other countries around the region and world, as well."