(CNN) The State Department's inspector general on Tuesday requested an urgent briefing with senior congressional staff members after Secretary of State Mike Pompeo pushed back on House Democratic demands to turn over documents related to Ukraine and to depose current and former State officials, according to sources briefed on the matter.

State inspector general Steve Linick plans to "provide staff with copies of documents related to the State Department and Ukraine" Wednesday afternoon in a bipartisan closed-door briefing with relevant congressional committees, a person familiar with the briefing told CNN.

The briefing comes amid the House Democrats' impeachment investigation, which has been fueled by the US Intelligence Community's inspector general's review of a complaint by a whistleblower who alleged President Donald Trump sought help from Ukraine's government to interfere in the 2020 elections.

One congressional aide described the State inspector general's request as "highly unusual and cryptically worded."

The inspector general said the reason for the briefing was the office had obtained documents from acting legal adviser in the State Department. The briefing comes as the House committees investigating Trump and Ukraine have delayed one of those depositions planned for this week, according to an aide, but former US special envoy to Ukraine Kurt Volker will appear Thursday.

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