NAIROBI, Kenya — Amid reports that there were unheeded warnings of a terrorist attack on Nairobi's Westgate shopping mall, turf wars between police and army units and friendly fire fatalities, a Kenyan parliamentary committee has summoned security chiefs to explain what went wrong.

The security officials are expected to appear at a committee hearing next week, according to news reports Friday.

"The time for responsibility and accountability has come," the committee chairman, Ndung'u Gethenji, told reporters.

The Daily Nation newspaper has reported on arguments over who was in charge, and confusion and jostling between various Kenyan security agencies ordered to respond to the mall attack that began Sept. 21, lasted several days and left at least 72 people dead. The Kenya Red Cross Society says 61 people remain missing.

Some security units went into the building — where hundreds were trapped by gunmen — with a mission to rescue a group of VIPs, the newspaper reported. There was no confirmation of who the VIPs were, but those inside at the time included President Uhuru Kenyatta's son, the president's sister and her son and the son's fiancee. Kenyatta's nephew and the fiancee died.

During the crisis, the first response from Kenyatta and others in the political elite was a call for Kenyans to pull together. In an address to the nation on the mall crisis, Kenyatta announced that police chief David Kimaiyo was in charge, to make the chain of authority clear.

As days have passed with little information on the fate of hostages and missing people, Kenyans' patience has frayed and people have begun demanding answers.

The Al Qaeda-linked Somali militant group Shabab claimed responsibility for the attack.

Several Kenyan news reports Friday cited sources saying that intelligence chief Michael Gichangi had warned police chiefs about a possible terrorist attack on the mall. Police denied the allegation in comments to the Daily Nation.

The Star and Daily Nation both reported that a pregnant woman was warned by her brother, an intelligence officer, not to visit the mall because it would be attacked. She usually shopped there on Saturdays.

Disputes over who was in charge delayed the rescue of civilians, according to local media.

"Inquiries by the Nation indicate that a coordinated rescue mission was badly delayed because of disputes between the Kenya Police and KDF [Kenya Defense Forces] officers commanding their units on the ground," the Daily Nation reported.

A police unit that had begun evacuating civilians had a group of militants pinned down near the Nakumatt Supermarket, the newspaper reported, but the officers walked out after their commander was killed by friendly fire from a Kenyan army unit.

"The pullout left a vacuum that apparently allowed the terrorists to regroup and move through the mall slaughtering many captives. It also allowed the terrorists to deploy heavy-caliber machine guns that they had not used in the earlier shootout," the report said. "The teams also appeared to have had different aims. One officer involved said that some units had a priority to locate and rescue a specific group of VIPs."

An unidentified Kenyan official reportedly told the Associated Press on Friday that the actions of the Kenyan military caused the collapse of a section of the mall, which may have buried some hostages and militants.

The official told the AP that Kenyan troops fired rocket-propelled grenades inside the mall, but did not explain what caused four explosions Monday. Many observers believe it is likely that the building collapse occurred after the explosions.

Interior Minister Joseph Ole Lenku had said that a mattress fire set by militants had structurally weakened the mall, causing its collapse. He retreated from that statement Wednesday, saying engineers were examining the causes, but he insisted that the number of hostages' bodies buried in the rubble was "insignificant."

The forensic investigation and excavation of the mall, to search for more bodies and to try to establish attackers' identities, is expected to take more than a week.

Forensic experts from the United States, Israel, Germany, Britain and Canada are involved in the investigation.

robyn.dixon@latimes.com

Special correspondent Soi reported from Nairobi and Times staff writer Dixon from Johannesburg, South Africa.