Four deafening explosions at lunchtime on Monday marked what was the beginning of the end of Kenya’s worst terror attack since the 1990s.

By this morning, Kenyan security forces had taken control of the Nairobi shopping mall where Islamist fighters had killed at least 62 people, and police were doing a final sweep of the building after all remaining hostages had been freed.

A burst of gunfire from inside the Westgate mall had broke the overnight silence as a military helicopter circled above.

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Late on Monday security forces said that most of the hostages had been released, but it remained unclear whether all of the attackers had been killed or detained. Hurried ranks of commandos could be seen charging into the upmarket shopping mall that has been the scene of a murderous stand-off with Kenyan authorities since it was stormed by Islamic militants on Saturday afternoon.

As troops moved into the four-storey building and helicopters circled overhead, a column of black smoke began to rise from the rooftop.

Inside the mall fighters loyal to the Somali Islamist militia al-Shabaab had barricaded themselves in. They were holding an estimated 30 hostages and had lit fires to confuse the troops.

One member of the Kenyan force said that at least two of the terrorists died in the ground-floor supermarket where much of the fighting has been concentrated. “They just blew themselves up,” the soldier said by phone from inside the security cordon.

The day had begun with exchanges of fire and an abortive attempt by Kenyan forces, assisted by Israeli units, to seize back control of the battered shopping centre.

The lunchtime blasts swelled the crowds of onlookers. By mid-afternoon there was the bizarre spectacle of Kenyan police launching tear gas at onlookers and firing warning rounds into the air while at the same time only 100 metres away soldiers were exchanging fire with the militants in the mall.

As acrid yellow clouds of gas swirled around the hillside overlooking the disaster scene, heavy-calibre weapons could be heard from the direction of Westgate and a handful of young Kenyans threw stones at the police. The frayed tempers were evidence of a bloody stand-off that has lasted longer than anyone had predicted. The death toll from the attack which had climbed to 69 was revised back down to 62 late in the day but the Kenyan Red Cross said that 63 people were missing.

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However, the number of UK citizens confirmed killed has continued to climb. Six Britons are now known to have died but that figure may rise further, the Defence Secretary Philip Hammond said.

There were also reports that a “white woman” was among the attackers killed on Monday but there was no official confirmation. Several survivors of Saturday’s killing spree recalled seeing a “European-looking woman” among the heavily armed militants who were separating Muslims from non-Muslims and killing scores of weekend shoppers.

This has fuelled speculation that the Briton Samantha Lewthwaite, dubbed the “White Widow”, and previously married to one of the London 7/7 bombers, was among the attackers.

A stream of confident predictions have flowed from Kenyan authorities but few have been borne out by events. On Monday night the Inspector General of the Kenyan police, David Kimaiyo, said two of the militants had been killed and “several others injured”.

“Taken control of all the floors,” he later tweeted. “We’re not here to feed the attackers with pastries but to finish and punish them.”

Kenya’s Interior Minister Joseph Ole Lenku said the evacuation of hostages “has gone very, very well” and that Kenyan officials are “very certain” that there are few if any hostages left in the building.

"Our forces are combing the mall floor by floor looking for anyone left behind. We believe all hostages have been released," Mr Ole Lenku said on Twitter.

Security sources suggested that this confidence was premature. So far the militants have proven better prepared and have succeeded in repelling a number of attacks.

Their durability has led security services to investigate the possibility that they may have had support from inside the mall – possibly a cache of arms or explosives deposited prior to the attack.

“They seem to have an arsenal with them,” said an official. “When these guys lit the fires it stopped us and we weren’t able to proceed.”

Adding to the sense that the attackers had received outside assistance, Kenya’s interior ministry reported that it had arrested “individuals” at the airport.

There was no official confirmation of the fate of the hostages, with Kenyan police earlier revising downward their estimate of the number being held from 30 to 10. Military planners had been using CCTV pictures of the interior of the complex to try to calculate both the numbers of terrorists as well as the position of hostages and members of the public still in hiding.

At the Oshwal centre, a Kenyan-Indian community centre and Jain temple, which has been offering emergency assistance to survivors as well as basic facilities for families awaiting news, there were only two wounded Kenyan soldiers on Monday.

The pillars of the underground car park, where volunteers, family and reporters have sheltered during the regular exchanges of fire nearby, have been plastered with pictures of the missing.

Among them was the smiling photograph printed on black and white paper of Ravi Ramrattan, a young man from the Caribbean, who was believed to be an alumnus of the London School of Economics. His body was among those identified in the Nakumatt supermarket.

He had initially maintained contact with friends on the outside through text messages and phone calls. One of his friends, who had volunteered to counsel survivors as he kept vigil for Mr Ramrattan, said that, trapped inside, he had kept asking when the rescue operation would reach him. When he stopped replying to messages it had been hoped that his phone’s battery was exhausted. It is not known exactly how and when he died.

Meanwhile, there was the suggestion the attackers were taking orders from Somalia. A spokesman from al-Shabaab in Somalia, Sheikh Ali Mohamud Rage, restated the group’s claim to the attack. In an audio file posted on a website, he said the militants had been ordered to “take punitive action against the hostages” if security forces tried to storm their way in.

Further reading:

The victims came from around the world. So did their killers

Was wife of 7/7 bomber among attackers?

Kenyans are more united in tragedy’s aftermath

The victims: The architect and his pregnant wife

Video: Amateur footage from Kenya shopping mall attack

Ian Birrell: How to fight al-Shabaab