Two wounded Kenyan security forces officers were carried out of the mall this morning after a barrage of gunfire was heard.

This afternoon brief volleys of gunfire were heard and Kenyan television reporters said they had been told by officials that they could soon be asked to move further back from the mall.

An Associated Press reporter, positioned just 330 yards from Westgate, tweeted that a huge blast went off inside it.

Jason Straziuso said: ‘I’m 300 meters from mall when blast went off. Eery silence afterward. One short gunfire burst.

‘That last big blast far larger than any explosion I’m last 30 hours. No idea what caused it.’

Prime Minister David Cameron said: ‘It is an absolutely sickening and despicable attack of appalling brutality.’

As the massacre unfolded witnesses described terrifying scenes in which men, women and children of all ages and nationalities were brutally cut down.

The mall, a popular haunt for rich Kenyans and expats, was dotted with bodies lying in pools of blood. Some victims were shot dead as they sat in their cars, while others have been left with horrific injuries.

Mr Cameron told the BBC: ‘Our thoughts are also with the Kenyan government and people at this time. These appalling attacks that take place, where the perpetrators do it in the name of a religion.. they don’t. They do it in the name of terror, violence, extremism and their warped view of the world. They don’t represent Islam or Muslims in Britain or anywhere else in the world.

‘We’ve offered the Kenyans help in terms of policing and advice and intelligence collaboration.’

Two Canadians, including diplomat Annemarie Desloges, and two French women have been confirmed as being among the dead, along with renowned Ghanaian poet and statesman Kofi Awoonor.

The US State Department also said four American citizens were reported injured.

In his address today Mr Kenyatta said: ‘I want every bereaved family to know that I and indeed all of us mourn with them. No-one should lose their life so needlessly, so senselessly. They shall not get away with their despicable and beastly acts. We will punish the masterminds swiftly and indeed very painfully.

Tragic: Annemarie Desloges, a Canadian diplomat seen here with her husband Robert Munk, was killed in the atrocity

‘We need to work together to fight the terrorist battle not just here in Kenya. This is not a Kenyan war, this is an international war and we need to join hands and work together to see it effectively destroyed.’

Jonathan Maungo, a private security guard, told Reuters: ‘They entered through blood, that’s how they’ll leave.’

It’s understood that security officials are probing the possible involvement of the fugitive ‘white widow’ of 7/7 London bomber Germaine Lindsay, Samantha Lewthwaite – a key Al Shabaab bomb-maker and fundraiser.

The BBC’s Anne Soy said: ‘This is an upmarket shopping mall – it’s one of the more exclusive ones in Nairobi. It often attracts foreigners and wealthy Kenyans, many of them of Indian descent. This is a situation which is cutting across race, tribes and nationalities.’

Terrified shoppers told of how they huddled in back hallways and prayed they would not be found by the militants.

When the way appeared clear, crying mothers clutching small children and blood-splattered men sprinted out of the four-storey mall.

At one burger restaurant, a man and woman lay in a final embrace after they had been killed, before their bodies were removed. Pop music was left playing.

Scramble: People crawl on their stomachs to safety as security forces keep a lookout at the Nairobi mall on Saturday

Witness Elijah Kamau said the gunmen told Muslims to stand up and leave and that non-Muslims would be targeted, as they began their attack.

The gunmen threw grenades and then opened fire, sending shoppers and staff fleeing for their lives.

Brit Amita Sharma today spoke of her fear for family and friends after hearing they had been caught up in the Nairobi shopping centre siege.

The 41-year-old, from Slough, had been visiting relatives in the Kenyan capital just two weeks ago and said she was stunned by news of the attack at the Westgate Mall.

The events manager said: ‘We’ve spoken to a family friend who hid in the mall’s supermarket for three hours.

‘Staff tried to protect all the customers in the shop by closing all the shutters to stop the attackers getting in.

‘It must have been terrifying for them all. My friend said she could hear all the gunshots and shouting going on outside.

‘Thankfully she was unharmed but she is still very shaken by what has happened.’

Eyewitness Fred Ngoga Gateretse, an official with the African Union, told The New York Times: ‘Believe me, these guys were good shooters. You could tell they were trained.’

Charles Karani, 41, an IT engineer, said: ‘I hid under a car with my daughters, and I saw the men line up maybe 40 people and ask them who was Muslim, and if they were to prove it by saying the name of the Prophet’s mother. Those who got it wrong were shot.

‘There was blood everywhere. Two ladies under the car with me had gunshot wounds on their legs.

‘Another Indian gentlemen was hit in the face by a bullet but he seemed not to be gravely hurt. Other people for sure are dead. I saw four people lying, not moving.

Terror: Armed police guide a woman carrying a child to safety at Westgate Shopping Centre

‘A grenade was thrown and it rolled near us, my daughter said, “Papa, there’s a  grenade” – but thank God it didn’t go off and I kicked it away.’

The gunmen wore white bandanas, Mr Karani said, and appeared to work in teams, each taking control of a different floor of the five-storey building.
He also said officials had confirmed to him that the attacker they arrested was a Kenyan Muslim convert.

Nahashon Mwangi was at work when he received a desperate telephone call from his son, pleading with him to rescue him from imminent death.

‘Dad, I have been shot in the neck and hand. I am bleeding. Come and help me please,’ his 21-year-old son said.

‘It took me about an hour to access the area,’ Mwangi said. ‘I was crying and pleading with the police to save my son. I remember shouting like a kid, crying and crying but they wouldn’t let me through.’

Relief finally came five hours later, when his injured son was among a group of people located and evacuated by security forces who were sweeping the mall shop by shop.

He was rushed to Nairobi’s Aga Khan University Hospital and was undergoing emergency surgery.

‘I pray that he will be OK,’ the shocked father said. ‘Why would these people do this to us?’

Another victim, mall worker Zipporah Wanjiru, emerged from the ordeal alive but in a state of total shock.

‘They were speaking some language I could not understand,’ she said of the attackers. ‘I could not understand anything – but the sound of their voices was scary.’

Many of the injured have been taken to Kenyatta National Hospital, at which a fire broke out this morning, according to reports. The blaze is said to have erupted in the baby unit, with those being cared for evacuated to safety.

To add to the chaos so many people gathered to watch the shocking drama develop that police had to use tear gas to disperse them, according to a Washington Post writer.

Speaking from Nairobi, Daniel Howden, reporter for The Independent, told The BBC that a ‘massive operation’ was still ongoing inside the mall this morning where the gang continued to hold an unknown number of people hostage.

Critical: A victim is wheeled into the Aga Khan Hospital in Nairobi for emergency treatment

Rescue: A woman is shipped to an ambulance in a shopping trolley by centre staff

Devastating: Injured people receive assistance from bypassers at the scene of the shooting

There was a suspected al-Shabaab attack which left five dead and three injured at a restaurant in the eastern city of Garissa in January, and in August last year one person was killed and six more were left injured in the Eastleigh area of Nairobi on the eve of a visit by Hillary Clinton, then the United States secretary of state.