Republicans managed to bring the U.S. House Democrats' impeachment investigation to a halt on Wednesday as around two dozen Republican House members stormed into a closed-door deposition with a Defence Department official. Democrats said the move compromised national security as some of them brought electronic devices into a secure room.

The Republican manoeuvre delayed a deposition with Laura Cooper, a senior Defence Department official who oversees Ukraine policy, until midafternoon. The interview began roughly five hours behind schedule, after a security check by Capitol officials.

As a series of diplomats have been interviewed in the probe, several of them detailing U.S. President Donald Trump's efforts to persuade Ukraine to investigate a political rival, many Republicans have been silent on the president's behaviour. But they have been outspoken about their disdain for Democrats and the impeachment process, saying it is unfair to them even though they have been in the room questioning witnesses and hearing the testimony.

"The members have just had it and they want to be able to see and represent their constituents and find out what's going on," said Ohio Rep. Jim Jordan, the top Republican on the House oversight and reform panel. That committee is one of three leading the investigation, and its members are allowed into the closed-door hearings.

Democrats deny that Republicans are being treated unfairly, noting they have had equal time to question witnesses and full access to the meetings. But they said the lawmakers — several of whom do not sit on one of the three committees — had compromised security at the closed-door deposition. The interviews are being held in what is called a Sensitive Compartmented Information Facility, or SCIF, which is a totally secure room where members can hear classified information.

Dep. Asst. Secretary of Defence Laura Cooper arrives for a closed-door meeting to testify as part of the House impeachment inquiry into President Donald Trump on Wednesday. (Patrick Semansky/The Associated Press)

Several lawmakers leaving the facility said that some of the Republicans had brought their phones, even though electronics are not allowed. All members of Congress are familiar with the protocol of the SCIF, since they are often invited to classified briefings, and there are several such rooms around the Capitol.

Lawmakers described a chaotic scene. Democratic Rep. Debbie Wasserman Schultz said she had just walked into the room when the Republican lawmakers blew past Capitol Police officers and Democratic staffers. The staff member who was checking identification at the entrance was "basically overcome" by the Republicans, she said.

"Literally some of them were just screaming about the president and what we're doing to him and that we have nothing and just all things that were supportive of the president," Wasserman Schultz said.

Republican Sen. Lindsey Graham criticized his Republican colleagues for the tactic, calling them "nuts" to make a "run on the SCIF."

"That's not the way to do it," he said.

The Republicans decried that the deposition was happening behind closed doors and said Americans should be able to read the transcripts of any interviews being conducted as part of impeachment.

A group of Republican House members stormed the secure room where the deposition was happening. (Yuri Gripas/Reuters)

Rep. Steve Scalise, the second-highest ranked House Republican, said Democrats are running a "Soviet-style process" that should "not be allowed in the United States of America."

"We're not going to be bullied," he said.

Democrats have promised to release the transcripts when it won't affect their investigation, and House intelligence committee chair Adam Schiff has pushed back on the criticism of the depositions.

Schiff said in a letter to colleagues last week that "the majority and minority have been provided equal staff representation and time to question witnesses, who have stayed until the majority and the minority have asked all of their questions — often late into the evening."

Several Republicans appeared to be tweeting from the secure room. North Carolina Rep. Mark Walker tweeted: "UPDATE: We are in the SCIF and every GOP Member is quietly listening." Georgia Rep. Buddy Carter wrote that "my Republican colleagues and I just stormed the impeachment hearing room and finally got in."

UPDATE: We are in the SCIF and every GOP Member is quietly listening. <br><br>Meanwhile, Adam Schiff, clearly peeved that he will no longer be able to hide his impeachment sham, is threatening Ethics punishment for all of us.<br><br>His fake intimidation can’t hide his lies–Open the process! —@RepMarkWalker We are sick and tired of this secretive, backroom impeachment sham. My Republican colleagues and I just stormed the impeachment hearing room and finally got in. However, Chairman Schiff got up and walked away. That's what cowards do, they get up and walk away. <a href="https://twitter.com/hashtag/StoptheSchiffShow?src=hash&ref_src=twsrc%5Etfw">#StoptheSchiffShow</a> <a href="https://t.co/trDb8P3pG6">pic.twitter.com/trDb8P3pG6</a> —@RepBuddyCarter

Arizona Rep. Andy Biggs retweeted some of his colleagues but followed up with a clarification: "All tweets sent out when I'm in the SCIF are being transmitted to staff for publication," he wrote.

The standoff came the day after a top U.S. diplomat testified that he was told Trump withheld military aid to Ukraine until the country's president went public with a promise to investigate Democrats. Democratic Rep. Ted Lieu of California said Republicans didn't want to hear from Cooper because they were "freaked out" by what (acting U.S. Ambassador to Ukraine) William Taylor told lawmakers.

"They know more facts are going to be delivered that are absolutely damning to the president of the United States," Lieu said.

As some members remained in the room, Democratic Rep. Steven Lynch said Democrats shouldn't call security to remove the Republicans because it would be "theatrics."

"Just having members hauled off, even though it might give some people great pleasure, I think we just have to handle it in a better fashion," Lynch said. "Hopefully, with some deliberations, cooler heads will prevail."