"For example, if any administration official, including any career official, were on television on Sunday, September 16, they would have said what Ambassador Rice said. The information she had at that point from the intelligence community is the same that I had at that point. Clearly, we know more about today than what we did."

While congressmen from both parties agreed that security at overseas U.S. diplomatic posts is crucial, and they expressed hope for a bipartisan solution, several times during the hearing the dialogue devolved into rancorous comments back and forth.

The assault in Benghazi occurred 11 years to the day after the September 11, 2001, attacks on New York's World Trade Center and the Pentagon.

Kennedy said the fullest picture of proper security and procedures will not be fully clear until a review board appointed by Secretary of State Hillary Clinton and including former Joint Chiefs Chairman Adm. Michael Mullen is completed.

Democrats had accused Issa of planning a partisan, election-year hearing, a similar allegation leveled against the panel for its past investigations of the botched "Fast and Furious" gun-running program and the failed Solyndra clean energy company that received government loan guarantees.

On Tuesday, two senior State Department officials provided reporters with the most detailed explanation yet of the attack in Benghazi, saying on a conference call that there was no prior indication such an assault was imminent.

The officials, who briefed reporters on condition of not being identified by name, said there was "nothing unusual" throughout the day of the attack.

Stevens held an evening meeting with a Turkish diplomat and then retired to his room in one of the compound's buildings at 9 p.m., according to the officials. The first sign of a problem came 40 minutes later, when diplomatic security agents heard loud talking outside the compound, along with gunfire and explosions.

Asked whether the attack was a spontaneous assault taking advantage of a demonstration, as originally asserted by Obama administration officials, one senior official said, "That was not our conclusion."

The two senior officials offered riveting detail of the attack by what one of them described as "dozens of armed men" who marauded from building to building and later fired mortars on a U.S. annex less than a mile away.

In the havoc at the four-building compound, Stevens and two of his security personnel took refuge in a fortified room that the attackers were able to penetrate, one official said.

The attackers doused the building with diesel fuel and set it ablaze and the three men decided to leave the safe haven and move to a bathroom to be able to breathe, according to the official. Stevens became separated from the security personnel in the chaos and smoke, and eventually turned up at a Benghazi hospital, where he was declared dead.