WASHINGTON -- The recent disclosure that Hillary Rodham Clinton relied on personal emails to conduct government business as secretary of state has breathed new life into a congressional panel investigating the Obama administration's handling of the 2012 attacks on the U.S. mission in Benghazi, Libya.

Benghazi has been a persistent Republican line of attack against President Barack Obama and Clinton, who is the favourite for the Democratic nomination in the 2016 presidential campaign. But the congressional investigation had threatened to stall amid accusations of partisanship on both sides.

The situation has changed since revelations about Clinton's email practices raises questions about whether she was complying with regulations requiring government officials to preserve written communications involving official business. Clinton exclusively used a private email account for government business during her time as secretary of state, and did so via a private server kept at her home.

Republicans on the Benghazi committee have become fixated on a photo that became an Internet meme -- Clinton, wearing sunglasses, staring at her BlackBerry.

Chairman Trey Gowdy wants to know why the panel has no emails from Oct. 18, 2011, the day the photo was taken as Clinton, then the secretary of state, was en route to Tripoli. In fact, the committee says it has no emails at all from Clinton's trip to Libya, which occurred just days before longtime Libyan ruler Moammar Gadhafi was killed.

Eleven months later, in September 2012, terrorist attacks on the U.S. mission in Benghazi killed U.S. Ambassador Chris Stevens and three other Americans.

Among other allegations, Republicans have accused the Obama administration of downplaying the role of al-Qaida figures at the time.

The latest congressional inquiry comes even though several other Republican-led House investigations debunked various conspiracy theories about the attacks. A 2014 report by the House Intelligence Committee determined there was no intelligence failure, no delay in sending a CIA rescue team, no missed opportunity for a military rescue and no evidence the CIA was covertly shipping arms from Libya to Syria.

Gowdy said in an interview that it "strains credulity" to believe that while on a trip to Libya to discuss Libyan policy "there's not a single document that has been turned over to Congress."

Gowdy has issued a subpoena for Clinton's emails and called for an independent review of Clinton's private email server. Republican House Speaker John Boehner, meanwhile, has not ruled out a vote in the full House to force Clinton to turn over her server.

Clinton has described her exclusive use of personal email as secretary of state as a matter of "convenience" and a way to avoid using two devices. She says she turned over more than 30,000 work-related emails to the State Department last year, at the agency's request. However, she said she got rid of roughly the same number emails because they were personal in nature.

The House Oversight and Government Reform Committee said it will send a letter Friday to the State Department and Clinton formally requesting answers to a series of questions about Clinton's emails.

Gowdy called the Libyan trip emblematic of "huge gaps" -- stretching for months -- in documents turned over to the committee by the State Department. "It's not up to Secretary Clinton to decide what is a public record and what is not," said Gowdy, who wants Clinton to appear before his committee at least twice: once to talk about emails and a second time to offer testimony on Benghazi.

Gowdy, a former prosecutor, denied claims by some Democrats that he is looking to expand the jurisdiction of the Benghazi committee to focus on Clinton, possibly slowing or derailing her presidential bid.

Rep. Elijah Cummings of Maryland, the senior Democrat on the Benghazi panel, called the dispute over Clinton's emails a distraction and said he hopes the Benghazi panel "will return to its purpose of investigating the attacks in Benghazi instead of attempting to impact the 2016 presidential election."