U.S. House of Representatives impeachment inquiry devolved into chaos on Wednesday as Republican lawmakers, encouraged by President Donald Trump to get tougher in fighting Democratic efforts to impeach him over dealings with Ukraine, stormed into a high-security hearing room and delayed testimony by a witness.

The more than two dozen Republican lawmakers, who were not authorized to attend the hearing, entered before Laura Cooper, the U.S. defence official who oversees Ukraine and Russia matters, was due to testify behind closed doors before Republican and Democratic lawmakers.

The Republicans yelled complaints that the Democrats in charge of the inquiry were conducting it in private, lawmakers and aides said. Republicans who are members of the three congressional committees conducting the inquiry have taken part in the process throughout.