Attack begins at midday local time on Saturday. Attackers enter building from front entrance, via second floor car park and reportedly also via the basement. Begin shooting and throwing grenades at fleeing shoppers. Hostages taken and reportedly held in cinema and Millionaires Casino.
2. Stand off
Approximately an hour into the attack, security forces enter the building. Gun battles ensue between police and the attackers, some of whom barricade themselves into the Nakumatt supermarket. Armed forces and helicopters are deployed, with gunfire and explosions continuing overnight.
3. Renewed assault
By Sunday, around 10-15 attackers remain inside the mall according to Kenyan authorities. Gunfire and explosions continue throughout the day. At 1845 two helicopters land on the roof in an apparent operation to retake the mall, and a large explosion from the inside is heard.
Security forces launch a renewed assault. Fire sweeps through parts of the building. Some interior floors and part of the floor of car park collapse. Sporadic gunfire heard by journalists early on Tuesday. By evening President Uhuru Kenyatta declares the siege over, giving a death toll of 61 civilians and six security officers.
Saturday 21 September
The attack on the Westgate Shopping Centre in Nairobi unfolded at around noon local time (0900 GMT).
The building was packed with shoppers and people having lunch.
The multi-storey, upmarket mall is owned by an Israeli businessman, has restaurants, cafes, banks, a large supermarket and a cinema.
The centre has six levels - with three devoted to shopping, eating and leisure, a third and fourth containing offices and a dental practice, with a basement underneath.
The BBC has established from senior security sources that in the weeks leading up the siege, the Islamists hired a shop in the mall.
This gave them access to service lifts, enabling them to stockpile weapons and ammunition.
When the attack began, the gunmen are thought to have entered the building from three points.
According to witnesses sitting outside ArtCaffe on the ground floor, one group armed with assault weapons drove up to the main entrance.
The attackers, dressed in black and wearing turbans, began firing and throwing grenades, causing panic as shoppers fled in any direction away from the gunfire.
|An image of the attackers inside the mall captured via CCTV|
Simultaneously, a second group made its way into the second floor of the building via a rooftop car park.
A children's cooking competition was taking place in the car park and a number of children and adults are believed to have been killed here, including the host, popular radio DJ Ruhila Adatia-Sood.
A third group of attackers is thought to have entered the building down a ramp to a basement area.
The exact number of attackers was initially estimated from 6-16.
Some witnesses say they were masked, and there are unconfirmed reports of the presence of Americans and a British woman among their number.
From the ground floor, witnesses reported that the first group made its way upwards through the mall shooting and throwing grenades.
According to some reports, the attackers made attempts to separate Muslims and non-Muslims, with Muslims allowed to leave the mall unharmed.
The BBC has established that the attackers set up a base using a ventilation shaft on the first floor.
A number of people are thought to have been taken hostage and held in a cinema and a casino on the second floor, while other unconfirmed reports suggest a number of people were held hostage in the basement area.
Police and security forces' response was initially slow, with some reports that the first officers on scene did not arrive until around 1230.
Security forces efforts initially focused on rescuing scores of people trapped inside, as gunfire and explosions continued to echo around the mall.
At around 15:00, Kenya Defence Forces (KDF) troops were deployed, entering the mall to confront the militants.
Gun battles raged throughout Saturday afternoon, with one group of attackers apparently barricading themselves in the two-level Nakumatt supermarket.
Having pre-positioned weapons in the preceding days, the attackers were able to re-arm quickly and repel Kenyan security forces
Late on Saturday, there was a change of tack by the militants, according to security sources. They rolled out heavy calibre machine guns, exploiting the moment control of the rescue efforts switched from the police to the military.
By the end of Saturday, the death toll stood at 39 with more than more than 1,000 people evacuated.
The security operation continued into the night with sporadic gunfire and explosions.
Sunday 22 September
Gunfire and explosions continued to echo around the mall on Sunday morning.
By midday - 24 hours after the attack began - the death toll stood at 59, with about 1,000 people rescued.
Interior Minister Joseph Ole Lenku said that between 10 and 15 attackers remained barricaded inside the mall, but that security forces had control of the CCTV room.
There are reports via the Israeli military intelligence analysis websiteDebkafile that Israeli security men were assisting the Kenyan military in the operation against the attackers.
At 1845 two helicopters were seen landing on the roof in an apparent effort to retake the mall. Shortly afterwards a large explosion was heard from inside.
Monday 23 September
On Monday morning, a series of loud explosions and heavy gunfire was heard and thick black smoke began billowing from the complex as security forces launched another assault.
Mr Lenku told journalists that almost all the hostages had now been evacuated - indicating that some remain unaccounted for - two of the militants had been killed and several had been injured.
He said 62 people had died but the security forces were now in control of every floor of the shopping centre.
As night fell, a fire was seen burning at the shopping centre and security forces continued the operation to clear the building of militants.
Early on Tuesday, a senior police source declared the operation to clear the building was "over", however journalists outside reported that sporadic gunfire was continuing.
The fire in the mall - which Kenyan officials said was started by the attackers burning mattresses - caused part of the building's roof to collapse.
Video footage showed that part of the car park on the second floor roof had completely collapsed, with a pile of rubble and smouldering vehicles visible below.
The confirmed death toll is 61 civilians, six security officers and five militants.
Investigators are working to establish the identity of the dead attackers, and whether one of them was female.
It is thought that the death toll could rise, with bodies possibly concealed under the rubble.
Kenya's Standard Newspaper reported that dozens of bodies were removed on Tuesday evening, while Kenya's Red Cross has said that 61 people remain unaccounted for.
However Interior Minister Joe Lenku has said that he does not expect the toll to rise significantly.
Responsibility for the attack has been claimed by al-Shabab - an Islamist group based in neighbouring Somalia, which is part of the al-Qaeda network.
Al-Shabab has said via Twitter that 137 hostages died after government troops used chemical agents to end the siege, but its statement cannot be verified and the government has denied its claims.
New photos revealing some of the damage at the Westgate shopping centre were released on Friday.