This post was last updated at 5:25 p.m. ET.

A standoff that began with a shocking attack at Kenya's Westgate Mall Saturday is in its second day, with civilians held hostage by gunmen in the upscale shopping center.

The authorities say they have isolated the attackers. As of Sunday afternoon, Red Cross officials reported 68 deaths and at least 200 wounded in the assault, with 49 people still missing. We'll add news to this post as it emerges.

"The priority is to save as many lives as possible," Kenyan Interior Cabinet Secretary Joseph Lenku tells the AP. He said that about 1,000 people have been rescued since the standoff began.

Update at 6:15 p.m. ET: Tweet Claims List Of Attacker Names

Earlier today, a now-suspended Twitter account that claimed to be al-Shabab, the group that has claimed responsibility for the attack, released a list of names of those it says were the attackers. The list had some of the names, along with an age, next to American cities.

A senior State Department official told NPR on background that they "have seen the reports, are not in a position to confirm, and are seeking further details."

Update at 5:25 p.m. ET: Possible Gains By Kenyan Force

It seems that the government force has made gains. But it's still too early to say with certainty when the standoff might end.

"Most of the hostages have been rescued and security forces have taken control of most parts of the building," the Kenya's National Disaster Operation Center says.

But the agency followed up that message by saying, "All efforts are underway to bring this matter to a speedy conclusion."

The agency also notes that four members of the Kenyan Defense Forces were injured and have been taken to the hospital.

Update at 4:00 p.m. ET: Rescue Operation Ongoing

As the evening wears on in Nairobi, reports from journalists and officials maintain that Kenyan forces are working to end the standoff and free the hostages. It is now nearing midnight in Nairobi, which is seven hours ahead of Eastern Time in the U.S.

AP correspondent Jason Straziuso reported hearing a large explosion about an hour ago. He then added a description of the mall, saying that its bottom floor was lit, while the upper floors were dark.

"Rescue operation at the Westgate Mall is still underway," Kenya's National Disaster Operation Center wrote in a tweet after 3 p.m. ET. "Hostage situations are delicate and must be handled with utmost care and caution."

That message followed on the heels of another that proclaimed a looming end to the standoff:

"This will end tonight. Our forces will prevail. Kenyans are standing firm against aggression, and we will win."

Update at 1:40 p.m. ET: President Obama Calls Kenyan Leader

President Obama called President Uhuru Kenyatta Sunday morning to express condolences for Saturday's terrorist attack.

During the call, President Obama told Kenyatta that his nation has U.S. support in bringing the attackers to justice, and to fighting terrorism, the White House says.

Update at 12:40 p.m. ET: 'Major Engagement' At The Mall

"Godspeed to our guys in the Westgate building. Major engagement ongoing. Sporadic gunfire," Kenya's National Disaster Operation Center says in a tweet. The message may bolster earlier reports that authorities had planned a sustained assault.

Night has fallen in Nairobi, and journalists have been either pushed back from the mall or restricted in what they can show from the scene, making it difficult to confirm what some news agencies had predicted would be an assault on the mall's attackers.

Update at 11:50 a.m. ET: Gunfire, Explosion Reported, Helicopters Flying Low

There are signs of activity among the government forces gathered outside Westgate Mall.

Shortly after 11 a.m. ET, news outlets reported that helicopters flew low over the building, and that gunshots could be heard.

About 20 minutes later, at least one large explosion was reported. TV news outlets that had been carrying live feeds from near the mall began showing images only from locations far from its exterior.

Before those events, Kenya's Citizen TV reported that police were tightening security in the area and rerouting traffic away from the mall, as well.

Update at 10:45 a.m. ET:Kenyan President Describes Losses, Attackers

In an address broadcast live Sunday, President Uhuru Kenyatta provided some details about the perpetrators of the attack.

"We have reports of women as well as male attackers. We cannot confirm details on this. Our security analysts are looking at that," he said. He said that the attackers are "located in one place within the building."

"The al-Shabab terror group have claimed responsibility for this cowardly act of terror, on social media," Kenyatta said. "However, investigations are underway to conclusively establish those responsible for this mayhem, so that we can have full accountability. They shall not get away with their despicable and beastly acts."

Kenyatta said it is "remarkable and encouraging" that more than 1,000 people have already been taken to safety from the mall since the violence began. He also expanded on his statement Saturday, that he lost family members in the attack.

"As your president, and as a leader, and also as a Kenyan, I feel the pain of every life we have lost, and share your grief at our nation's loss," Kenyatta told his nation. "My nephew and his fiancée were amongst those who died in this attack."

The government's forces at the mall face a balancing act of pursuing the attackers and ensuring the safety of the hostages, Kenyatta said. And he said the attack is part of a bigger conflict.

"This is not a Kenyan war," he said. "This is an international war."

Update at 9:40 a.m. ET: British Nationals Died In Attack

The violence in Nairobi has killed three British nationals, the U.K. Foreign & Commonwealth Office said Sunday. A spokesman from the office added, "The number of British Nationals confirmed as killed is likely to rise as further information becomes available."

British officials say "a rapid deployment team" has been sent from London to Nairobi to support the consulate.

Our original post continues:

Saturday's assault started with grenades that were thrown around lunchtime, the peak foot-traffic period, officials say. Panic then ensued, as gunmen began firing indiscriminately. Reports indicate that groups of gunmen attacked different areas simultaneously, in a coordinated strike. The attack has been celebrated by al-Shabab, a militant group based in Somalia, which claimed responsibility for the attack.

Lenku said the number of attackers is between 10 and 15. He did not estimate the number of hostages remaining in the mall. Kenyan officials say that on a normal weekend, about 10,000 people shop at the mall, which is popular among foreigners and the wealthy.

On Sunday, police and Kenyan Defense Forces troops patrolled the area outside the mall and tried to disperse crowds that had gathered in the streets adjacent to the building. For the second day in a row, officials released tear gas to move bystanders from the scene.

"Waiting ambulances are parked outside while sporadic gunfire can be heard coming from inside Westgate Mall," NPR's Gregory Warner reports from Nairobi. "Kenyan police said that the gunmen have been 'contained' but there are still hostages in unsecured locations. Special police forces are securing the building."

Gregory adds, "It's the deadliest terror attack in Nairobi since the U.S. Embassy bombings of 1998."

The attack met with widespread condemnation Sunday, with leaders of France, Britain, Canada and other nations offering their condolences and aid.

The violence has also touched the lives of those in power in Kenya. On Saturday, the country's President Uhuru Kenyatta told those who lost a loved one, "I know what you feel, having also personally lost very close family members in this attack."

And several Americans are among the wounded, according to the U.S. State Department.

"Although we have no reports of any Americans killed today, we have lost a member of our own State Department family," Secretary of State John Kerry said in a statement, "the wife of a foreign service national working for the U.S. Agency for International Development."

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