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."