Laura Petrecca -- USA TODAY
Multiple barrages of gunfire erupted Sunday morning from the upscale Kenyan mall where there is a hostage standoff with Islamic extremists nearly 24 hours after they attacked using grenades and assault rifles.
Two wounded Kenyan security forces were carried out of the Westgate shopping mall after a sustained volley of gunfire that may have included grenade blasts.
Kenyan authorities said the militants held an unknown number of hostages in the shopping center located in the Westlands area of Nairobi, after killing at least 59 on Saturday. The attack is believed to be orchestrated by extremists against non-Muslim Kenyans and Westerners in the area.
Kenya's interior cabinet secretary Joseph Lenku said that 175 were injured and that about 1,000 people have been rescued so far.
Somali militant group al-Shabaab claimed responsibility on Twitter for the deadly shooting, which was allegedly carried out by 10 to 15 gunmen with AK-47s and other sophisticated weapons. Al-Shabaab said the attack was retribution for Kenyan forces' 2011 push into Somalia and threatened more violence.
"The Mujahideen entered #Westgate Mall today at around noon and are still inside the mall, fighting the #Kenyan Kuffar inside their own turf," the group said on Twitter.
"What Kenyans are witnessing at #Westgate is retributive justice for crimes committed by their military," the group said.
Americans were among those injured at the Westgate mall shooting, according to a statement from Marie Harf, deputy spokesman for the State Department.
"We have reports of American citizens injured in the attack, and the U.S. Embassy is actively reaching out to provide assistance," she said. "Due to privacy considerations, we have no further comment on American citizens at this time." No Americans were reported killed.
In a separate statement, a White House spokeswoman said some staff at the U.S. Embassy in Kenya have been "tragically affected" by the attack. No other information was provided.
"The perpetrators of this heinous act must be brought to justice, and we have offered our full support to the Kenyan Government to do so," Caitlin Hayden, a spokeswoman for the White House National Security Council, said in the statement.
In a statement issued Sunday, Secretary of State John Kerry described the attack as "a heartbreaking reminder that there exists unspeakable evil in our world which can destroy life in a senseless instant."
The attack killed the wife of a foreign service national working for the U.S. Agency for International Development, according to the statement.
"While we mourn with her family today, we also pledge our commitment to do whatever we can to assist in bringing the perpetrators of this abhorrent violence to justice, and to continue our efforts to improve the lives of people across the globe," Kerry said.
Kenyans and foreigners were among those confirmed dead, including French and Canadians. Kenyan President Uhuru Kenyatta said he lost some family members in the attack.
Kenya's presidential office said that one of the attackers was arrested on Saturday and died after suffering from bullet wounds.
"Violent extremists continue to occupy Westgate Mall. Security services are there in full force," said the United States embassy in an emergency text message issued Sunday morning.
Trucks brought in a fresh contingent of soldiers from the Kenya Defense Forces early Sunday to back the combined military and police force that surrounded the upscale mall.
Lenku said that there are 10 to 15 attackers involved. He said that Kenyan forces have control of the mall's security cameras.
Kenyan media reported that several people in hiding in the mall escaped to safety, suggesting that not everyone who is still inside is being held by al-Shabab.
Cecile Ndwiga said she had been hiding under a car in the basement parking garage.
"I called my husband to ask the soldiers to come and rescue me. Because I couldn't just walk out anyhow. The shootout was all over here - left, right- just gun shots," she said.
Nairobi resident Paolo Abenavoli said he is holed up in his apartment only 100 meters from the mall with a direct view of the entrance. He said he could see a dozen or more security forces inside a first floor restaurant.
"The battle is on now," Abenavoli told The Associated Press by telephone as the fresh gunfire broke out Sunday.
Security forces had pushed curious crowds far back from the mall. Hundreds of residents gathered on a high ridge above the mall to watch for any activity.
The attack began on Saturday afternoon, according to Kenya's Daily Nation. Gunmen tossed grenades and opened fire as panicking shoppers fled the building, some jumping down one story from the second floor of the mall to escape, witnesses told the paper.
Nairobi Police Chief Benson Kibue deemed the shooting "a terrorist attack."
Witnesses told local and national news media that the gunman asked Muslims to leave before opening fire. Kenya is 83% Christian with a sizable Muslim community - about 11% of its 44 million people.
The gunmen carried AK-47s and wore vests with hand grenades on them, Manish Turohit, 18, who hid in a parking garage for two hours, told the Associated Press.
"They just came in and threw a grenade. We were running and they opened fire. They were shouting and firing," he said after marching out of the mall in a line of 15 people who all held their hands in the air.
Off-duty Sgt. Major Frank Mugungu told the AP that he saw four male attackers and one female, and that he could clearly identify one of the gunmen as a Somali, though he could not identify the rest.
Military cordoned off the building in the heart of the upscale Westlands district, which is home to upper-class Kenyans and expatriate Westerners - many of whom work for the United Nations - and a locale frequented by tourists.
A local organization was hosting a party for children at the Israeli-owned Westgate mall on Saturday. The mall is also a popular nightspot for hip, young Kenyans who gather there to watch movies or eat at restaurants there.
It is on Kenya's watch list as a site for attacks, along with its towering conference center and Western hotels such as the Hilton.
Like most shopping mall complexes in Nairobi, it is manned by security personnel at its entrance, checking bags and shoppers with metal detectors. But locals noted repeatedly in the aftermath of the attacks that these are just cursory checks and that the security guards are no match for armed gunman.
Still, security in the city is tight because of prior attacks in the past two decades, including one on the U.S. Embassy by al-Qaeda in 1998 that killed more than 200 people. Besides the threat of terrorism, the city faces its own internal threats - sometimes called "Nairobbery" - arising from extreme poverty and income inequality.
Crime and corruption are among the biggest concerns of the locals. The city is one of the most dangerous urban areas in sub-Saharan Africa. Although the situation is better than a decade ago, most middle-class and wealthy urban dwellers refrain from walking on city streets after dark, a situation that has led to the popularity of the city's shopping malls in its rich western districts as quasi-entertainment centers.
Contributing: Jabeen Bhatti from Berlin; the Associated Press