Kenya has begun three days of national mourning following the end of the four-day siege by Islamist militants on Nairobi's Westgate shopping centre. In a televised address, President Uhuru Kenyatta said six members of the security forces were among 67 people who had died. Declaring the siege over, he said five militants had been killed and 11 other suspects arrested. As the clearing of the mall continues, the number of dead is expected to rise. Several bodies, including those of some attackers, are thought to be trapped under rubble after three floors of the building collapsed following a blaze. Kenya's Standard newspaper reported that tens of bodies were removed from the building on Tuesday evening. Correspondents say the shopping centre lay largely silent overnight and light smoke was still drifting from the building. 'Stared down evil' Journalists and onlookers were kept behind a security cordon but police let some people retrieve cars from the scene. In his address, the president praised the response of ordinary Kenyans, calling it exemplary and overwhelming. "We have ashamed and defeated our attackers," he said. "Kenya has stared down evil and triumphed." He did not confirm earlier reports that some of the attackers were US and British. "Intelligence reports had suggested that a British woman and two or three American citizens may have been involved in the attack," said Mr Kenyatta. "We cannot confirm the details at present. Forensic experts are working to ascertain the nationalities of the terrorists." He added: "These cowards will meet justice, as will their accomplices and patrons, wherever they are." At least 18 foreigners are among the dead. They include six Britons as well as citizens from France, Canada, the Netherlands, Australia, Peru, India, Ghana, South Africa and China. About 175 people were wounded including 62 who remain in hospital. Somali Islamist group al-Shabab said it had carried out the attack in retaliation for Kenyan army operations in Somalia. The militants stormed the Westgate centre on Saturday, throwing grenades and firing indiscriminately on shoppers and staff. "Now it is for the forensic and criminal experts," said police spokesman Masoud Mwinyi. A Twitter post from al-Shabab on Tuesday dismissed claims that women were involved in the attack. The group said: "We have an adequate number of young men who are fully committed and we do not employ our sisters in such military operations." Al-Shabab, which is linked to al-Qaeda, has repeatedly threatened attacks on Kenyan soil if Nairobi did not pull its troops out of Somalia. There are about 4,000 Kenyan troops in the south of Somalia as part of an African Union force supporting Somali government forces. Al-Shabab is fighting to create an Islamic state in Somalia. Despite being pushed out of key cities in the past two years, it remains in control of smaller towns and large swathes of the countryside. UN special representative for Somalia Nicholas Kay called on Tuesday for a fresh surge in African troops to Somalia to counter an estimated 5,000 al-Shabab fighters.