Police in Kenya grew irritated as people took to social media to describe what they were seeing and hearing.
"If you must Facebook or tweet, then talk about football or your favourite music but NOT MISINFORM the public on security operations!" authorities said on Twitter.
Three injured security forces were taken out of the besieged mall, but the severity of their injuries was unclear.
By Sunday afternoon, at least 1,000 people had been freed from the mall, Kenyatta said. But some 30 people were believed to still be held.
Later, that number fell to no more than 10, military spokesman Cyrus Oguna told CNN affiliate KTN.
"The number that is still left in the building is very, very small," he said, without providing details on how people got out.
One apparent hostage left the building Sunday, and said she had been hiding in the basement of the mall, KTN reported.
Al-Shabaab vowed not to negotiate with Kenyan authorities.
"The Mujahideen are still strong inside #Westgate Mall and still holding their ground," the group tweeted late Saturday.
Israeli special forces were at the scene and were working with their Kenyan counterparts in the hostage crisis, Kenyan government sources told CNN.
Kenyatta said several nations had offered help but "this remains an operation of the Kenya security agencies."
State House spokesman Manoah Esipisu said there were reports of a white woman among the hostage takers. Kenyan intelligence officials were investigating the claims, he said.
Esipisu was asked if the reported woman was thought to be the infamous Al-Shabaab-affiliated "White Widow," Samantha Lewthwaite. "Nothing is being ruled out," he said.
But CNN terrorism analyst Peter Bergen said it was unlikely.
"It would be very unusual for a woman to be involved in one of these operations," he said. "Typically these groups are misogynist. Their view is the woman should be in a home and shrouded in a body veil."
Lewthwaite's husband, Germaine Lindsey, was one of the suicide bombers killed in the 2005 attack on London's transportation system. His Buckinghamshire-born widow is wanted by Kenyan authorities for her alleged role as an Al-Shabaab and al Qaeda-linked financier.
A day of horror
The calm was shattered around noon local time Saturday. Gunshots erupted as shoppers picked up groceries, savored lunch and browsed through the racks at stores.
Before long, pools of blood smeared pristine hallways. Bodies lay strewn across the floor.
Uche Kaigwa-Okoye was sipping coffee when he heard what first sounded like a fallen table, then the continuing rat-a-tat of gunfire. As the gunshots became louder, screaming crowds headed for the exits.
He joined 20 people who took shelter for about five hours in a women's bathroom cubicle.
"They had grenades, and it was really, really loud," he said of the attackers. He noticed tear gas in the hallways as well.
"All of us felt like they were close," he said.
As people texted family and friends outside the mall, word spread that nobody could be trusted. And even if the good guys could be sorted from the bad guys, the intermittent barrages of gunfire made any escape attempt seem futile.