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.