WASHINGTON -- A CIA security team rushed to the U.S. consulate in Libya’s eastern city of Benghazi less than 25 minutes after receiving the first call that the mission was under attack, while a second squad was dispatched by air from the capital, Tripoli, according to a timeline released on Thursday by U.S. intelligence officials.

The timeline is the most detailed accounting to date of the U.S. response to the attack on the consulate and was released to rebut news reports that U.S. officials had delayed a rescue.

“The officials on the ground in Benghazi responded to the situation . . . as quickly and as effectively as possible,” said a senior intelligence official, speaking on condition of anonymity. “There were no orders to anybody to stand down in providing support.”

The timeline also revealed that a nearby CIA annex came under attack twice during the events, with the second assault coming more than seven hours after Islamist extremists first stormed the consulate.

Four Americans died in the assaults: U.S. Ambassador to Libya Christopher Stevens and State Department computer specialist Sean Smith, who died at the consulate, and two former Navy SEALs, Tyrone Wood and Glen Doherty, who were working as security contractors in Libya.

The events have become an issue in the U.S. presidential election campaign, with Republicans accusing the Obama administration of failing to provide adequate security to the mission amid mounting threats by al Qaida-linked militants and other groups.

Republican nominee Mitt Romney and others also have questioned the administration’s initial account that the assault was a spontaneous outgrowth of a protest against an online video denigrating the Prophet Muhammad, and not a pre-planned terrorist attack launched to mark the anniversary of the Sept. 11, 2001, attacks on the United States.

The Office of the Director of National Intelligence later accepted responsibility for the administration’s initial account, acknowledging that the attackers were Islamist militants, including some suspected of having ties to al Qaida’s North African affiliate.

According to the timeline, the first call for help from the consulate was received at the CIA’s nearby Benghazi headquarters – referred to as a diplomatic annex by U.S. officials – at around 9:40 p.m., which is when the attack began.

“Fewer than 25 minutes later, a security team left the annex for the mission,” said the timeline, which added that the group spent about 25 minutes trying to take out militants firing heavy weapons as it fought its way to the walled compound and then entered it under heavy fire.

At 11:11 p.m., according to the timeline, an unmanned surveillance drone arrived over the complex while the CIA security team, which comprised about six officers, rounded up the approximately 30 staff members on the consulate premises and prepared to move them to the annex. The security team at that point had recovered Smith’s body but had been unable to locate Stevens, who local Libyan guards had spirited out a backdoor to a local hospital, where he was pronounced dead from smoke inhalation.

The CIA security team and the mission staff drove out of the consulate under fire and returned to the annex, which had come under sporadic small arms and rocket-propelled grenade fire.