UAE's ailing President Sheikh Khalifa dies aged 73

UAE President Sheikh Khalifa bin Zayed Al-Nahyan died Friday aged 73 after a years-long battle with illness, triggering a period of mourning and a handover of power in the oil-rich Persian Gulf state.

Sheikh Khalifa, who was in office during a time of rocketing fortunes for the United Arab Emirates but was rarely seen in public, was laid to rest in Abu Dhabi's Al Bateen Cemetery just hours after his death was announced, in accordance with Muslim tradition.

Sheikh Khalifa's funeral prayers were conducted by his expected successor and half-brother Mohamed bin Zayed, who has long been viewed as the country's de facto ruler.

"The people of the Emirates are united in grief as we mourn the loss of our leader and President, Khalifa bin Zayed," tweeted Mohamed bin Zayed, often known as "MBZ".

The most visible testament to Sheikh Khalifa is the world's tallest building, Dubai's Burj Khalifa, which was renamed after he bailed out the debt-hit emirate when the global financial crisis struck in 2009.

Flags flew at half-mast above the interior ministry in Abu Dhabi and other landmarks at the start of 40 days of official mourning, with work suspended in the public and private sectors until Tuesday.

Sheikh Khalifa took over as the UAE's second president in November 2004, succeeding his father as the 16th ruler of Abu Dhabi, the richest of the federation's seven emirates.

He has made few public appearances since 2014, when he had surgery following a stroke, although he has continued to issue rulings.

The cause of death was not immediately released.