Special counsel Robert Mueller's investigators have subpoenaed the Trump campaign for documents from a number of people as part of his probe of Russian interference in last year's election campaign, a source with knowledge of the investigation told Fox News late Thursday.

The subpoena, which was issued last month, was first reported by the Wall Street Journal.

The Journal reported that the special counsel's office is seeking documents and emails from more than a dozen campaign officials that reference certain Russia-related keywords. The paper described it as Mueller's first official order for the Trump campaign to produce information.

The source described the subpoena to Fox as a "cleanup operation" aimed at collecting any missing information and ensuring that Mueller had the same documents as the three congressional committees conducting their own investigations.

Separately, the top Republican and Democrat on the Senate Judiciary Committee said earlier Thursday that White House Senior Adviser Jared Kushner -- President Trump's son-in-law -- hasn't been fully forthcoming with the panel's probe into Russian election interference, asking him to provide emails sent to him involving WikiLeaks and a "Russian backdoor overture and dinner invite."

Senate Judiciary Chairman Chuck Grassley, R-Iowa, and Sen. Dianne Feinstein, D-Calif., sent a letter to Kushner's lawyer saying the collection of documents he has provided the committee is "incomplete." The committee gave Kushner a Nov. 27 deadline to provide the additional documents, including the emails and Kushner's security clearance form that originally omitted certain contacts with Russian officials.

The senators noted they have received documents from other campaign officials that were copied to or forwarded to Kushner, but which he did not produce. Those include "September 2016 email communications to Mr. Kushner concerning WikiLeaks." Trump's eldest son, Donald Trump Jr., corresponded with WikiLeaks that month and, according to The Atlantic, sent an email to several Trump campaign advisers to tell them about it.

Grassley and Feinstein wrote that other parties have produced documents concerning a "Russian backdoor overture and dinner invite" that Kushner forwarded but has not given to the committee. It is unclear what overture and dinner invite they are referring to.

The senators are also asking Kushner for correspondence with former national security adviser Michael Flynn, who is a subject of an investigation by Mueller.

Abbe Lowell, Kushner's lawyer, said in a statement that Kushner has been "responsive to all requests."

"We provided the Judiciary Committee with all relevant documents that had to do with Mr. Kushner's calls, contacts or meetings with Russians during the campaign and transition, which was the request," Lowell said. "We also informed the committee we will be open to responding to any additional requests and that we will continue to work with White House Counsel for any responsive documents from after the inauguration."

The new request is a sign that the panel is still moving forward with its probe into the Russian interference and whether Trump's campaign was involved.

In the letter to Kushner, the senators noted they had asked him to provide documents to, from, or copied to him "relating to" certain individuals of interest to investigators, but Kushner responded that no emails had been found in which those individuals were sent emails, received emails, or were copied on them.

"If, as you suggest, Mr. Kushner was unaware of, for example, any attempts at Russian interference in the 2016 presidential election, then presumably there would be few communications concerning many of the persons identified in our second request, and the corresponding burden of searching would be small," the senators wrote.

The committee also asked for the additional documents related to Flynn, detailing a long list of search terms, and rebuffed Kushner's lawyer's arguments that his security clearance is confidential and unavailable because it has been submitted to the FBI for review.

The Senate and House intelligence committees interviewed Kushner in July. The Judiciary panel has also sought an interview with Kushner, but his lawyers offered to make the transcripts available from the other interviews instead, according to the letter. The senators say those panels haven't provided them with those transcripts, and ask Lowell to secure that access.

Then "we will consider whether the transcript satisfies the needs of our investigation," Grassley and Feinstein wrote.

Fox News' John Roberts and the Associated Press contributed to this report.

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