NAIROBI (AFP) - Most of the hostages trapped in a Nairobi shopping mall by Islamist gunmen have now been rescued and most of the complex is secure, the Kenya army announced late Sunday.

"Our concern is to rescue all hostages ALIVE and that is why the operation is delicate," the Kenya Defence Forces said in a situation update on Twitter.

"All efforts are underway to bring this matter to a speedy conclusion," it said.

The army said four of its soldiers were wounded in the latest fighting inside the upmarket Westgate mall, which was stormed by gunmen from Somalia's Al-Qaeda-linked Shebab rebels midday on Saturday.

At least 68 people have been killed and 200 wounded in the attack, officials said.