All hostages held in a Nairobi mall by Islamic militants appear freed, officials said Tuesday, as Kenya\'s foreign minister said the gunmen included Americans. The hostage-rescue claim came after security forces mounted a major assault to free the people still believed inside the upscale Westgate Premier Shopping Mall. \"We believe all hostages have been released,\" the Kenya National Disaster Operation Center said in a Twitter message without giving the number of hostages freed. \"Special forces and KDF soldiers combing the building. Situation of hostiles to be confirmed,\" the Twitter message continued. KDF stands for Kenya Defense Forces. At least 62 people were reported killed in the siege and at least 175 people, including children as young as 2, were seriously injured. The Somali-based al-Shabaab fundamentalist militia, which is part of al-Qaida, claimed responsibility for the attack, which started around 1 p.m. Saturday when 10 to 15 armed assailants rushed into the mall from three entrances and opened fire. Its spokesmen said the attack was revenge for Kenya\'s decision to send thousands of troops to help the neighboring Somali government fight al-Shabaab Islamic insurgents two years ago. At least two attackers in the Nairobi attack were killed, police said. Among the attackers was a Caucasian-looking woman in a headscarf with an AK-47 assault rifle who fired on shoppers as they fled and dived for cover, a Western security officer briefed on the assault told The Wall Street Journal. That woman is alleged to be Samantha Lewthwaite, a British soldier\'s daughter who converted to Islam and became known as the White Widow after her husband, Germaine Lindsay, was killed as one of the suicide bombers in the July 7, 2005, London bombings. The coordinated London attacks on the city\'s mass transit during the morning rush hour killed 52 civilians and injured more than 700 others. Al-Shabaab boasted in a Twitter message the White Widow was with them. \"Sherafiyah lewthwaite aka samantha is a vrave [sic] lady! were happier to have her in our ranks!\" said the group, whose Twitter has been repeatedly closed down. If Lewthwaite participated, she might have escaped shortly after the attack started, security officials in Nairobi indicated. The officials were quoted by The New York Times as saying two female militants who appeared to be directing other assailants during the killings were among the assault ringleaders who managed to get away after the attack\'s initial stage, blending in with a crowd of fleeing civilians. Kenyan Foreign Minister Amina Mohamed also spoke of a female British jihadi Monday but didn\'t identify Lewthwaite by name. She told the \"PBS NewsHour\" the British woman involved in the attack on the luxury mall was known to have \"done this many times before.\" Government officials in London had no immediate comment. Mohamed also said \"two or three Americans\" were among the assailants. She identified them as men, 18 to 19 years old, of Somali or Arab origin, who lived in Minnesota and another U.S. location. \"That just goes to underline the global nature of this war that we are fighting,\" she said. State Department spokeswoman Jen Psaki told CNN the administration had \"no definitive evidence of the nationalities or identities of the perpetrators,\" adding the department was pressing to determine if any assailants were American. Somali leaders in Minnesota moved quickly to distance their community from the attacks. \"The safety and security of the United States is of utmost importance to Somali-Americans, and we are committed to be in the forefront of defeating extremism,\" Abdisalam Adam, an imam of the Islamic Civic Society of America, was quoted in the Star Tribune of Minneapolis as saying in a news conference with other Somali religious leaders Monday. \"This kind of activity, killing innocent people, has no base or any relationship with Islam,\" said Abdirizak Hashi, an imam at Abubakar As-Saddique Islamic Center in Minneapolis. President Obama said Monday the United States stands with Kenya\'s leadership \"against this terrible outrage that\'s occurred.\" He called al-Shabaab \"one of the most vicious terrorist organizations in the world.\"