Former United States Secretary of State Hillary Clinton speaks during a news conference at the United Nations headquarters in New York March 10, 2015. [Photo/Agencies]

WASHINGTON - The photo that became an Internet meme - Hillary Rodham Clinton, wearing sunglasses, staring at her BlackBerry - troubles Republicans on the House committee investigating the deadly attacks in Benghazi, Libya.

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 US mission in Benghazi killed US Ambassador Chris Stevens and three other Americans.

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."

The recent disclosure that Clinton relied on personal emails to conduct government business has breathed new life into the Benghazi panel's investigation, which had threatened to stall amid accusations of partisanship on both sides.

Clinton is the clear front-runner for the Democratic nomination in the 2016 presidential campaign, but the controversy has upended her careful blueprint for the rollout of her campaign. Clinton had planned to spend March touting her work on women's issues and giving a handful of paid speeches before announcing her candidacy in early April.

In the past week alone, 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, setting up a high-stakes confrontation between the Republican-led Congress and Clinton.

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."

The committee's turn in the spotlight comes just a few weeks after Democrats complained that the Benghazi investigation was moving at a "glacial" pace and that Gowdy was leading the panel on increasingly partisan path. In late January, Gowdy vowed to "ratchet up" an inquiry he said was being hobbled by resistance from the Obama administration.

The inquiry comes after several 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.