The dead toll in Saturday's  armed attack on a shopping center in Kenya's capital Nairobi has reached 59, while the number of injured currently stands at 175.

The Kenyan Ministry of Interior has stated that the most probable cause is a terrorist attack.

1 000 people had managed to escape from the upscale Westgate center after the assault, suspected to be carried out by al-Shabab militants. Between 10 to 15 attackers are believed to be still in the building. The number of civilians trapped there - either as hostages or hiding from the militants – remains unknown.

The BBC reports Sunday heavy military presence both in and around the shopping center, and sporadic gunfire heard from inside.

The gunmen are believed to be currently holed up in a supermarket.

Kenyan President Uhuru Kenyatta earlier vowed to "hunt down the perpetrators wherever they run to".

Kenyan officials said "major operations" were underway with police and soldiers preparing an apparent bid to bring an end to the stand-off.

They said the security forces had finally "pinned down" the surviving gunmen.

Al-Shabab told the BBC it carried out the attack in response to Kenyan military operations in Somalia.

There are about 4 000 Kenyan troops in the south of Somalia, where they have been fighting the militants since 2011.