Gunfire has been heard inside a besieged mall in Nairobi, suggesting that at least one of the terrorists who laid siege to the Westgate shopping centre is still in the building.

At daybreak Kenyan security forces launched a major attack against al-Shabaab militants who are holding hostages inside the mall. Military helicopters hovered over the upmarket mall in Kenya's capital and sustained gunfire broke out inside.

A military spokesman had earlier said that "most" of the hostages had been released.

At least 69 people have been killed and more than 170 injured since 10 to 20 Islamic insurgents broke into the four-storey mall with grenades and assault rifles on 21 September.

More than 60 people are missing, according to the Red Cross

Al-Shabaab, a Somali Islamist group linked to al-Qaida, has claimed responsibility for the attack on Twitter.

The group also used social media to name the attackers, suggesting many were foreign fighters coming from the US, Canada and Britain.

Below are the latest images from in and around the shopping centre. WARNING: SOME READERS MAY FIND GRAPHIC IMAGES BELOW DISTURBING.

Westgate Mall Nairobi
Soldiers from the Kenya Defence Forces (KDF) are seen entering the Westgate Shopping Centre in the capital Nairobi Reuters
Westgate Mall Kenya
A Kenyan soldier holding a dog by its leash enters the main gate of the Westgate Shopping Centre in Nairobi Reuters
Kenya Westgate seige
A man donates blood at a temporary donation centre for injured victims in Nairobi Reuters
Nairobi mall
A man reads a daily newspaper with other onlookers at the edge of a security perimeter Reuters
Nairobi Westgate seige
Relatives and Muslim faithful bury an 18-year-old who was killed in crossfire between armed militants and the police at the Westgate shopping mall Reuters
Westgate Mall Kenya
Onlookers stand along the road and look from a distance at the Westgate Shopping Centre Reuters
Kenyas President Uhuru Kenyatta
Kenya's President Uhuru Kenyatta addresses the nation; his nephew is among those killed in the terrorist attack Reuters
Westgate Mall Nairobi
Security officers take cover near the Westgate shopping mall during the third day of stand-off between Kenyan security forces and al-Shabaab gunmen Reuters
Westgate Mall Nairobi seige
Security officers walk past members of the media stationed on the edge of a security perimeter to head towards the Westgate Shopping Centre Reuters
Twitter Kenya