NAIROBI  (AFP) – Kenyan troops have launched an assault on cornered Somali militants holding hostages inside a Nairobi shopping mall to end a deadly siege, the government crisis team said Sunday.

“Godspeed to our guys in the Westgate building,” Kenya’s National Disaster Operation Centre said in a message on its Twitter site. “Major engagement ongoing.”

An image grab taken from AFP TV shows Kenyan troops taking position on September 21, 2013 inside the Westgate mall in Nairobi. Kenyan troops were locked in a fierce firefight with Somali militants inside an upmarket Nairobi shopping mall

The number of people killed in the ongoing siege, which began on Saturday, is feared to rise sharply from the 59 people confirmed dead, police sources said after entering the building.

“We fear the death toll… it could be much, much higher than what we have, judging from the bodies sighted inside,” a police officer said, after reports from inside of multiple corpses.

“There are more people dead inside, and some of the attackers are still armed and throwing grenades and shooting at the officers,” the officer added.

The disaster centre reported “sporadic gunfire”, while an AFP reporter outside the mall said a loud explosion had been heard as troops moved inside the sprawling complex.

Military and police helicopters were also reported flying overhead the mall.