Kenya mall attack: About 30 hostages still inside, sources say NEW: 1,000 people have been freed, a government official says He says between 10 and 15 gunman are involved The death toll reaches 59; at least 165 people are hospitalized Al-Shabaab, an al Qaeda-linked militant group in Somalia, claims responsibility Nairobi, Kenya (CNN) -- Twenty four hours. Fifty nine dead. About 30 hostages still inside. Those are the grim numbers a day after attackers stormed an upscale Nairobi mall, spraying bullets and holding shoppers captive. By noon Sunday, as grim-faced Kenyan soldiers warily searched the five-story building -- and as al-Shabaab maintained its defiant stance -- the siege was no closer to a resolution. Kenyan government and Western diplomatic sources said al Shabaab militants were holding about 30 hostages inside the shopping center. Officials believe 10 to 15 gunmen are involved, State House spokesman Manoah Esipisu said Sunday. "We know that they were across the building," Esipisu told CNN's Zain Verjee. We know that they are now isolated somewhere within the building. The attack has already left 59 people dead, government minister Joseph Ole Lenku said Sunday. Another 175 were injured. It was the deadliest terror attack in the nation since al Qaeda blew up the U.S. Embassy in 1998, killing more than 200 people. The attack Saturday targeted a popular weekend meeting spot. Kenyans and expatriates gather at the luxurious Westgate mall on weekends to drink lattes, catch a movie or browse through the more than 80 stores. Al-Shabaab, al Qaeda's proxy in Somalia, claimed responsibility, and said it was not backing down. In a message on its Twitter feed, the group said "all Muslims" were escorted from the mall before the attack. "When justice is denied, it must be enforced," it said in a tweet Sunday. Kenyans were relatively safe in their cities before they invaded us & killed Muslims #Westgate As the sun rose Sunday, the standoff between Kenyan forces and the attackers continued. Soldiers kept vigil outside the mall, guns dangling from their shoulders. "We want to do everything possible, and the security people are doing everything possible to make sure we lose no more lives," Esipisu said. Many unknowns Three injured security forces were taken out of the besieged mall, but the severity of their injuries was unclear. By mid-day Sunday, at least 1,000 people had been freed from the mall, Esipisu said. Our priority is now those that remain inside. An apparent hostage left the building Sunday, and said she had been hiding in the basement of the mall, CNN Affiliate KTN reported. The attackers targeted the luxurious mall on an especially crowded day. Wealthy Kenyans and expatriates gather there on weekends to drink lattes, catch a movie a or browse through the more than 80 stores. Al-Shabaab, an al Qaeda-linked militant group based in Somalia, claimed responsibility for the bloodshed and vowed not to negotiate with Kenyan authorities. The group said "all Muslims" were escorted from the mall before the attack. "The Mujahideen are still strong inside #Westgate Mall and still holding their ground," the group tweeted late Saturday. 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 barrage of intermittent gunfire made any escape seem futile. Sara Head, a Washington resident, experienced similar horror in the mall's parking garage. As her car pulled up, she heard gunfire. She crawled underneath and hid behind cars before getting into a stairwell. Eventually, the stairwell lights came back on and the door to a nearby supermarket opened. She dashed through, passed a nearby loading dock and fled to safety. "There was blood throughout the supermarket," Head said. It wasn't clear if it was OK to exit. The national disaster agency reported early Sunday morning that five "visibly shaken" hostages had been released. It said "major operations underway." What that meant was a mystery. Foreigners among casualties Most of the casualties are Kenyan, authorities said. But the mall is popular with expatriates and foreign nationals, who were among those killed and injured. That includes two dead French nationals and two Canadians, including a diplomat, their governments said. Several American citizens were among the wounded, including Elaine Dang, a University of California, Berkeley graduate. Dang worked as the general manager for Eat Out Kenya, which confirmed her injuries on its Twitter and Facebook pages. The State Department said Saturday there were several Americans among the injured, but none among the dead. Secretary of State John Kerry didn't offer details. The U.S. Embassy is asking personnel to stay in place Sunday and avoid the Westgate Mall area and any large gatherings. All U.S. citizens in Kenya are urged to register online so the embassy can provide them with updated information on travel and security -- and can contact them in case of emergency. Israel's Foreign Ministry said one national was slightly wounded and three escaped. A cafe at the mall is owned by an Israeli, but the ministry does not believe the mall was targeted because of that. The Ghana president's office said literary figure Kofi Awoonor was among those killed in the attack. "Such a sad twist of fate to place prof at the wrong place at the wrong time," President John Mahama said in a statement. A plea for blood Several Kenyan agencies made a plea for blood donations. "Hospitals are appealing for more blood, the response is incredible but more is needed," tweeted Francis Kimemia, secretary to the Cabinet. And as the nation grappled with the aftermath, Kenya's president blasted "the despicable perpetrators of this cowardly act," and said they will be brought to justice. We shall hunt down the perpetrators Kenya is no stranger to terrorism. A 1998 bombing at the U.S. Embassy in Nairobi left 213 dead. Al Qaeda claimed responsibility for the attacks. Since Kenya launched attacks against the Al-Shabaab in Somalia in 2011, the group has hurled grenade attacks at Kenyan churches, bus stops and other public places. In a televised speech late Saturday, Kenyatta said his nation has "overcome" such attacks before, refusing to budge from its values or relinquish his security. And it will do so again, he promised. "We shall hunt down the perpetrators wherever they run to," the president said. We shall get them, and we shall punish them for this heinous crime. But first, authorities will have to get to all the assailants and hostages still inside the mall. CNN's Faith Karimi, Holly Yan and Greg Botelho reported and wrote from Atlanta; Lillian Lesposo reported from Nairobi. CNN's Tim Lister, Nima Elbagir, Joseph Netto, Boriana Milanova, Jamie Crawford, Stefan Simons, Karen Smith and Azadeh Ansari contributed to this report.