Government troops have killed two more gunmen in a fresh assault on the Nairobi shopping mall.

Westgate Mall was rocked by four large blasts as soldiers sought to rescue shoppers who have been held by al-Qaida-linked militants for the last three days.

Military and police helicopters circled over the mall as the explosions were followed by volleys of gunfire, then thick, dark smoke.

Kenyan authorities said they would do their utmost to save hostages’ lives, but no officials could say how many people were being held captive. Kenya’s Red Cross said the death toll rose to 68 after nine bodies were recovered on Sunday. More than 175 people were injured, including many children.

Security forces’ efforts the previous day to rescue the hostages inside failed despite the military announcing that “most” had been saved. Kenyan officials have said preserving the hostages’ lives is a top priority, greatly complicating the rescue effort.

Kenyans and foreigners were among those confirmed dead in the attack by up to 15 gunmen. They included British, French, Canadians, Indians, a Ghanaian, a South African and a Chinese woman. The UK Foreign Office said Monday it has confirmed the deaths of four British nationals.

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From neighbouring Somalia, spokesman Sheik Ali Mohamud Rage for al-Shabab - the militant group that claimed responsibility for the attack - said that the gunmen had been ordered to “take punitive action against the hostages” if force was used to try to rescue them.

Al-Shabab militants reacted angrily on Sunday to the helicopters hovering over the mall, and warned on Twitter that the Kenyan military action was endangering hostages.

A large military assault began on the mall shortly before sundown on Sunday, with one helicopter skimming very close to the roof of the shopping complex as a loud explosion rang out, far larger than any previous grenade blast or gunfire volley. Officials said the siege would soon end and said “most” hostages had been rescued and that officials controlled “most” of the mall. But on Monday the stand off remained.

As the crisis surpassed the 48-hour mark, video taken inside the mall’s main department store when the assault began emerged, showing frightened shoppers crouching as long and loud volleys of gunfire could be heard.

The al-Shabab extremists stormed the mall on Saturday from two sides, throwing grenades and firing on civilians.