BAGHDAD, Iraq (CNN) -

The United States "has no reason to doubt" the authenticity of a video that purports to show ISIS leader Abu Bakr al-Baghdadi delivering a sermon at the Great Mosque of al-Nuri in Mosul, two U.S. officials said.

While the United States cannot absolutely guarantee it is the notoriously elusive leader of the Islamic State of Iraq and Syria, the working assumption by the government is that it is him, according to the officials who spoke on condition of anonymity.

If it is al-Baghdadi, it may just reveal how comfortable the ISIS leader is after his fighters took control of Iraq's second-largest city.

"Iraqi agencies are still investigating the video and comparing it with its intelligence," Iraq's military spokesman, Lt. Gen. Qassim Atta, said on Monday.

ISIS, an al Qaeda splinter group, has seized large areas of northern and western Iraq in an offensive that began last month.

Al-Baghdadi is known to the United States as Ibrahim Awad Ibrahim Al Badry. He was taken into custody in Fallujah in the Anbar province on February 4, 2004, according to a Pentagon statement.

There have been mixed reports about when and why he was detained. He was held until the following December at a a prison at Camp Bucca, according to the Pentagon. A review board recommended his "unconditional release," the statement said.

While the Pentagon said al-Baghdadi was from Fallujah, other reports have said he is from Samarra, north of Baghdad.

Parliament postponed

State-run Iraqiya TV said Monday that Parliament has been postponed for at least a month, a day before lawmakers were scheduled to return to form a new government and begin the process of selecting a prime minister.

Citing sources in Parliament, Iraqiya reported that the session was postponed until August 12 because the political parties have been unable to reach a consensus on who to name to country's top leadership posts. Those include the speaker, the president and the prime minister.

A week ago, Iraq's Parliament postponed its first session, citing a lack of a quorum after 90 lawmakers walked out.

Suicide car bomb in Baghdad

A suicide car bomb exploded in heavy traffic at a security checkpoint in Baghdad's Kadhimiya neighborhood on Monday, killing at least seven people and wounding 14, security officials told CNN. The death toll is expected to rise, they said.

The bomb exploded at about 1 p.m. near the checkpoint, which created a sort of bottleneck of traffic. The explosion occurred less than mile (1 kilometer) from the Kadhimiya shrine, which is revered by Shiites.

The bombing follows a double bombing last week in the same area that killed at least 25 people and wounded 32.

Iraqi security forces commander killed

A Twitter account widely believed to be linked to the ISIS in Salaheddin province claimed in a post that its fighters killed an Iraqi military commander.

According to the post, Iraqi Army Col. Ibrahim Abdullah Hussein was killed. It posted what it claimed was a picture of Hussein's corpse as well as a photograph of his ID card.

CNN cannot independently confirm the claim. Some militant groups are known to release pictures of ID cards as evidence of deaths.

British ambassador: Baghdad warned repeatedly

Britain's ambassador to Iraq says Prime Minister Nuri al-Maliki's government was warned repeatedly over the past several months about the threat posed by the Islamic State of Iraq and Syria.

"The fact that Mosul was vulnerable was known," Ambassador Simon Collis said on CNN's Amanpour show.

"The fact that ISIL were already holding territory from last year in parts of western Iraq, in Anbar, and elsewhere was well known."

Collis said Britain's message to al-Maliki's government was always the same: "Any comprehensive counterterrorism strategy would need a political line of operation, an economic and development line of operation, as well as of course security operations."

He continued, "And without that kind of comprehensive approach, it will be impossible to defeat an organization like ISIL."

ISIS is also referred to as the Islamic State of Iraq and the Levant.

Iraqi general killed

The commander of the Iraqi Army's 6th Division was killed in a battle on Monday, according to a statement released by the Prime Minister's office.

He was identified as Gen. Nagm Abdullah Ali. The statement did not detail how he died.

But Atta is quoted by Iraqi news organizations as saying he was killed in shelling in Ibrahim Bin Ali, a Sunni-dominated village about 16 miles north of Baghdad.

CNN could not independently confirm the claim.

Digging in around Baghdad

A commercial airliner roars overhead as one of the thousands of fighters who have taken up arms to protect the Iraqi capital digs into a position a few miles from Baghdad International Airport.

Every 500 feet (150 meters), another fighter armed with an AK-47 assault rifle takes up another position about 2 miles (3 kilometers) from the airport perimeter.

This is the first line of seven similar concentric lines of defense between the outskirts of the capital and the airport, widely believed by Iraqi and U.S. officials to be a top target of ISIS.

The fighters are members of the Badr Brigade, the Iranian-trained militia of the Supreme Council for the Islamic Revolution in Iraq, a powerful Shiite political party in Iraq.

And they are officially taking up arms for the first time in more than a decade, reinforcing Iraq's military.

It was just one of the signs Monday of stepped-up security in and around Baghdad amid fears that ISIS fighters and allied Sunni insurgents already inside the city will launch attacks, such as a bombing campaign.