Heavy gunfire and explosions have been heard at the shopping centre in Nairobi where militants are said to be holding a number of hostages.
Sixty-eight people have been killed and more than 170 injured since the attack began in Kenya’s capital on Saturday.
Between 10 and 15 attackers – thought to be militants from the Somali al-Shabab movement – are still inside the Westgate shopping centre.
Reporters at the scene said there had been heavy and rapid bursts of fire.
An unnamed Kenyan security source told the AFP news agency that an army assault was underway.
An AFP correspondent at the scene said he heard about 15 minutes of fierce gunfire which then subsided.
The International Criminal Court (ICC) announced on Monday morning it was adjourning the trial of Kenya’s Deputy President William Ruto on charges relating to violence following elections in 2007.
The court said Mr Ruto would be excused for a week to return to Nairobi to help deal with the crisis.