Corrections and clarifications: A previous version of this story gave the incorrect state for Rep. Tim Burchett. Burchett represents Tennessee’s 2nd Congressional District.

WASHINGTON – About three dozen Republican lawmakers protested how House Democrats are conducting the impeachment inquiry of President Donald Trump and temporarily halted the testimony of Defense Department official Laura Cooper Wednesday.

A chaotic scene unfolded after Republicans gave speeches and then pushed through the confines of the Capitol complex basement, to make their way into the secure room. Several Capitol police officers stationed themselves outside the secure room, as reporters waited outside for lawmakers to come back out.

Cooper, who serves as the deputy assistant secretary of defense for Russia, Ukraine, and Eurasia, was subpoenaed for a closed-door session with the House Intelligence, Foreign Affairs, and Oversight and Reform committees. She was expected to answer questions about how military aid was withheld from Ukraine as Trump sought the investigation of his political rival.

But Cooper's session was delayed for hours after the scheduled 9:30 a.m. start because Republicans who aren't members of the three key committees sought to attend. The deposition began about 3:15 p.m., according to a committee official and Rep. Val Demings, D-Fla.

After about three and a half hours of testimony, the shortest so far out of the depositions, Cooper left the SCIF later Wednesday evening.

Under House rules, only members of the committees and their staffers have been allowed in the private sessions that the committees have been conducting for weeks. But Republicans – mostly from committees that weren't allowed to attend – gave speeches in the hallway outside the secure room complaining about the lack of access and transparency. Then about two dozen lawmakers demanded entry.

Intelligence Committee Chairman Adam Schiff, D-Calif., left the room with Cooper during the commotion.

“I think they’re just trying to figure out a way procedurally to continue with the deposition,” Rep. Stephen Lynch, D-Mass., said of Republican and Democratic leadership of the committees. “Cooper’s on hold."

Rep. Eric Swalwell, D-Calif., said the protest was an “effort to intimidate witnesses who seek to come forward; the witness was in the hearing room at the time that Republicans started to come in.”

Rep. Ted Lieu, D-Calif., said Republicans were trying to enter the secure area while carrying electronics, which aren't allowed, and despite not being on the relevant committees.

“They also brought in their cellphones, which is a violation; they violated house rules by trying to crash committees,” Lieu said.

Swalwell said Republicans may have compromised the security of the room by bringing in electronics that could be tainted in ways that benefit adversaries.

“They may have brought in the Russians and the Chinese with electronics into a secure space,” Swalwell said.

Republicans said they respected the electronics policy, but the protest reflected their frustration with the closed-door meetings.

Rep. Mark Meadows, R-N.C., said he collected phones from his colleagues and brought them back out.

“You certainly want a secure environment but at the same time I think everybody wants to hear exactly what's going on," Meadows said.

Rep. Tim Burchett, R-Tenn., said none of the members took photos. “That would be illegal,” he said.

The sergeant at arms was summoned, but Meadows said it was unlikely anything would come of that.

Rep. Mark Walker, R-N.C., tweeted that Republicans were in the secure room and listening quietly, but that Schiff was "clearly peeved that he will no longer be able to hide his impeachment sham, is threatening Ethics punishment for all of us."

The Republican protest occurred in the Capitol Visitor Center, a complex of underground offices adjoining the Capitol Building, where the depositions have been held. Republicans denounced the inquiry as a “charade” held by Schiff in the "bunker of the basement of the Capitol," in the words of Rep. Jim Jordan of Ohio.

"The American people understand fairness and they instinctively know that what is happening here is not fair," Jordan said.

Rep. Mike Waltz of Florida, one of the Republicans who isn't on the key committees and who later attempted to enter the room, said special forces soldiers abroad were “ashamed” of the process for distracting from other issues. Rep. Debbie Lesko, R-Ariz., said the impeachment process was “unconscionable” and demanded a House vote to authorize the inquiry.

The protest was similar to smaller incidents conducted last week by Rep. Matt Gaetz, R-Fla., and House Minority Leader Kevin McCarthy, R-Calif.

Congressional investigators wanted to ask Cooper, who oversees Ukraine policy, about why the administration withheld military aid at a time when Trump was urging Ukraine President Volodymyr Zelensky to investigate former Vice President Joe Biden and his son, Hunter.

Bill Taylor, the top U.S. diplomat in Ukraine, told lawmakers Tuesday about the linkage between the aid and investigations.

Cooper received a subpoena to appear before the House committees on Wednesday, according to a senior Defense Department official who was not authorized to speak publicly. Late last week, Cooper had received a voluntary request to appear. She hired a private lawyer to represent her.

Meanwhile, Pentagon lawyers continue to review thousands of pages of documents subpoenaed by the House, the official said. The Pentagon will not release material If the White House counsel asserts executive privilege.

The chairmen of the three key committees – Schiff; Rep. Eliot Engel, D-N.Y., for Foreign Affairs; and Rep. Carolyn Maloney, D-N.Y., for Oversight – sent a letter Wednesday to John Sullivan, the deputy secretary of state, restating their demand for subpoenaed documents that the department has refused to provide.

The letter noted that the committees have already obtained correspondence before and after Trump’s call July 25 to Zelensky, diplomatic cables about Trump withholding military aid to that country and text messages or other electronic communications from witnesses in the inquiry. But the chairmen warned that the continued refusal to comply with their subpoena could be considered obstruction of Congress.

“These documents include information central to the inquiry’s core area of investigation: the President’s efforts to press Ukraine to initiate investigations that would benefit his personal and political interests, and not the national interest,” the chairmen wrote.

The White House has vowed not to cooperate with the impeachment inquiry, and has called it a "partisan" effort and a "coup."

Contributing: Savannah Behrmann