Republican politicians furious about being left out of the Donald Trump impeachment process have stormed a closed-door witness deposition and refused to leave.
The action is the latest in an escalating showdown over the investigation of the United States President.
More than two dozen politicians barged into a secure US Capitol meeting room known as a SCIF, delaying the testimony of a Pentagon official.
The Pentagon official is the latest witness in the Democrats' investigation of possible abuse of power by Mr Trump over his pressure campaign against Ukraine.
Republican Matt Gaetz departs after he and two dozen other Republican lawmakers stormed into the room used by the House of Representatives. Source: AAP
It is a violation of US House rules to access SCIFs - secure facilities designed to prevent electronic eavesdropping - without permission, and concerns were raised the politicians were committing serious security breaches by striding in with their mobile phones.
Some of the Republican politicians began tweeting from within the SCIF.
"BREAKING: I led over 30 of my colleagues into the SCIF where (House Intelligence Committee chairman) Adam Schiff is holding secret impeachment depositions. Still inside - more details to come," tweeted rebel leader congressman Matt Gaetz, a fierce Trump defender.
A follow-up tweet suggested Mr Gaetz was aware of the sensitivities of devices in the SCIF: "**Tweet from Staff**," it read.
The move, which Democrats branded a "stunt," delayed the deposition of Laura Cooper, a deputy assistant secretary of defence responsible for Ukraine policy.
All members of the three House committees conducting the investigation, Democrats and Republicans alike, are permitted to attend the depositions and question witnesses.
Republican Steve Scalise speaks to the media after he and two dozen other Republican lawmakers stormed the hearing. Source: AAP
Congressman Alex Mooney, who stormed the SCIF with Mr Gaetz, said in an audio recording posted online that Mr Schiff "saw us, took the witness and walked out of the room because they refused to have a hearing in a transparent way."
Republicans opposed to impeachment appear to have settled on a new strategy to fight back: attacking the process itself, claiming it is invalid because the House has not taken a floor vote to launch an impeachment inquiry, and that it lacks transparency.
The Republican protest came two days after Mr Trump urged his party to "get tougher and fight" against the investigation.
House Democrat Stephen Lynch said Republicans were seeking to "disrupt" the hearing to focus on the process rather than the substance of witness testimony.
They "wanted to exercise a right that doesn't exist," Mr Lynch told CNN.
