Kenyan Westgate siege
Kenyan security forces move in on al-Shabaab militants in Nairobi's Westgate shopping mall (Reuters)

Four Britons have been confirmed dead in the Islamic militant attack on an upscale Kenyan shopping mall.

Ross Langdon, who held joint British and Australian citizenship, died alongside his partner, Harvard-educated Elif Yavuz who was two weeks away from giving birth.

Malaria specialist Yavuz, who was born in the Netherlands, was working for the Bill and Melinda Gates Foundation in Kenya.

The pair were among 69 victims who have been killed in the attack launched by Somali militant group al-Shabaab.

UK defence secretary Philip Hammond said Britain "stood ready" to provide more assistance to Kenya as security forces tried to win back control of the Westgate shopping centre and free the remaining hostages.

Twenty explosions have been reported alongside outbursts of gunfire. Police and troops were "closing in", said Reuters. Thick smoke was pouring out of the mall on the third day of the siege.

It is not known how many militants were still holed up in the shopping centre or how many hostages they held.

Although Kenyan forces earlier said that most of hostages had been rescued, media reports, witnesses claimed that many civilians were still trapped inside.

The assailants have threatened to kill the detainees if attacked.

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