Eyewitnesses to September's deadly terrorist attack on the U.S. Consulate in Libya told a congressional committee Wednesday that State Department officials had blocked efforts to aid Americans under fire and later tried to conceal al Qaeda's involvement.

Mark Thompson, acting deputy assistant secretary for counterterrorism at the State Department, told the politically charged hearing that on the night of the attack he was stopped from mobilizing a foreign emergency support team that was specially equipped and trained to deal with emergencies like the one in Benghazi.

Thompson said White House officials told him directly that the emergency team would not be deployed because "it was not the right time and it was not the team that needed to go right then."

Thompson was among three State Department whistleblowers testifying before the Republican-led House Oversight and Government Reform Committee as part of lawmakers' ongoing effort to determine whether the U.S. government could have done more to save the lives of Ambassador Christopher Stevens and three other Americans killed during the Sept. 11 attack.

Republicans insist that the Obama administration misled the public about the nature of the Benghazi attack and then tried to cover up the deceit. They place particular blame on then-Secretary of State Hillary Clinton.

Gregory Hicks, the No. 2 diplomat in Libya who served directly under Stevens, said a second effort to send Special Forces to Benghazi that evening also was blocked. Those troops were told to stand down, he said.

Despite U.S. Ambassador to the United Nations Susan Rice's repeated claims immediately after the attack that it was a spontaneous response to an anti-Muslim Internet video, Hicks said it was clear from the beginning that the assault was coordinated and deliberate. He recalled receiving a phone call from the ambassador when Stevens told him, "We're under attack."

"The YouTube video was a nonevent in Libya," Hicks said.

Moreover, Hicks said, Rice's comments angered the Libyan government and made it harder to bring the FBI to Benghazi to secure the crime scene.

Hicks said he was told on Sept. 11 that fighter jets could arrive within three hours, contradicting the administration's claim that air support was eight hours away.

Republicans have refused to end their inquiry into Benghazi, much to the irritation of Democrats who claim the GOP is politicizing the attacks.

Committee Democrats, including Rep. Carolyn Maloney of New York, questioned the accuracy of the witnesses' testimony and defended the administration and Clinton.

Clinton has been under fire for approving a reduction in security in Benghazi before the attack. But she has testified that she did not personally see the cables from Stevens requesting additional forces.

Eric Nordstrom, the top security officer in Libya at the time, said the security in Benghazi was insufficient, with much of it left to Libyan forces that he believes were complicit in the attack.

"I think, to put it succinctly, it was the best bad plan," Nordstrom said. "It was the only thing we had."

Hicks said he was demoted after questioning Rice's claims about the attack in a series of Sunday talk shows, which he said left him "stunned" and "embarrassed."