In the most significant escalation yet in the wrangling between Congress and the FBI over the Trump dossier, the House Intelligence Committee has subpoenaed the bureau and the Justice Department for documents relating to the dossier, the FBI's relationship with dossier author Christopher Steele, and the bureau's possible role in supporting what began as an opposition research project against candidate Donald Trump in the final months of last year's presidential campaign.

The subpoenas are an indication of growing frustration inside the committee over the FBI and Justice Department's lack of cooperation in the Trump-Russia investigation.

The committee issued the subpoenas -- one to the FBI, an identical one to the Justice Department -- on August 24, giving both until last Friday, September 1, to turn over the information.

Neither FBI nor Justice turned over the documents, and now the committee has given them an extension until September 14 to comply.

Illustrating the seriousness with which investigators view the situation, late Tuesday the committee issued two more subpoenas, specifically to FBI Director Christopher Wray and Attorney General Jeff Sessions, directing them to appear before the committee to explain why they have not provided the subpoenaed information.

The subpoenas are the result of a months-long process of committee investigators requesting information from the FBI and Justice Department. Beginning in May, the committee sent multiple letters to the FBI and Justice requesting information concerning the Trump-Russia affair.

"We got nothing," said committee member Rep. Trey Gowdy, R-S.C., who is taking a leading role in the Russia investigation. "The witnesses have not been produced and the documents have not been produced."

In a telephone interview Tuesday, Gowdy said the FBI has said it needed more time to comply, and also that complying might interfere with the investigation of special counsel Robert Mueller. Whatever the reason, the documents haven't been produced.

"A subpoena is a tool of last resort in Congress," Gowdy, a former federal prosecutor, said