Standoff at Nairobi mall after gunmen kill at least 68 NAIROBI - More than 24 hours after Islamist militants stormed an upscale Nairobi mall, a tense standoff continued Sunday between the heavily armed assailants and Kenyan security forces, as the government announced that the death toll had risen to 68 with more than 175 injured in the deadliest attack in Kenya since the 1998 U.S. Embassy bombings. The attackers, strapped with grenades and wielding machine guns and AK-47 rifles, remained holed up inside the Westgate Premier Shopping Mall with as many as 30 hostages, Kenyan government officials said Sunday. An unknown number of people remained inside the building, hiding from the gunmen. Sporadic gunfire erupted at the mall Sunday morning as additional Kenyan security forces arrived to help defuse the crisis, which began Saturday afternoon. Late Sunday night, both Kenyan security authorities and al-Shabab, the Somali militia linked to al-Qaeda that claimed responsibility for the assault, said that a major security operation to end the siege was underway. In a tweet, Kenya's National Disaster Operations Center said, "Major security assault by security forces ongoing to end two-day siege at Westgate mall." In another tweet, the center said, "this will end tonight. Our forces will prevail. And al-Shabab in two tweets said: "Kenyan forces who've just attempted a roof landing must know that they are jeopardising the lives of all the hostages at #Westgate. The Kenyan government shall be held responsible for any loss of life as a result of such an imprudent move. The call is yours! Still, it was unclear whether the operation was an all-out effort to retake the mall or whether it amounted to another rescue operation to retrieve people trapped inside. Local news reports described several explosions coming from the mall, which has been cordoned off from the media and onlookers. In an earlier statement, Kenya's Red Cross said that 68 people had been killed and 49 people had been reported missing, but it was unclear whether this number included the hostages. A senior Kenyan Interior Ministry official, Joseph Ole Lenku, said that Kenyan forces had rescued about 1,000 people from the mall and that 10 to 15 attackers remained inside the shopping center. "The government will go out of its way to make sure we do not lose lives," Lenku told reporters. In a nationally televised news conference, Kenyan President Uhuru Kenyatta declared that the siege had a good chance of ending and urged the nation to be patient. The criminals are now located in one place within the building. With the professionals on site, I assure Kenyans that we have as good a chance to successfully neutralize the terrorists as we can hope for," he said. Kenyatta added that one of his nephews and his fiance were among those killed in the attack. Former Kenyan prime minister Raila Odinga told reporters that he had been told that the precise number of hostages inside the mall was unknown. "There are quite a number of people still being held hostage on the third floor and the basement area where the terrorists are still in charge," Odinga said, according to the Associated Press.