The UAE's long-time de facto ruler Sheikh Mohamed bin Zayed Al Nahyan was elected as president on Saturday, official media said, a day after the death of former leader Sheikh Khalifa.

Sheikh Mohamed was elected by the Federal Supreme Council, WAM news agency said, becoming the ruler of the oil-rich country founded by his father in 1971.

Sheikh Mohamed, often known as 'MBZ', met members of the Federal Supreme Council, made up of rulers of the UAE's seven emirates, as the oil-rich country enters a period of mourning for his half-brother Sheikh Khalifa.

His ascension, which was widely expected, formalises his position as leader of the desert state of 10 million after years of calling the shots while Sheikh Khalifa was sidelined by poor health.

Under his low-key direction, the United Arab Emirates has put a man in space, sent a probe to Mars and opened its first nuclear reactor, while using its oil-funded clout to develop a more assertive foreign policy.

Closely allied with Saudi Arabia, it has emerged as a leader of a reshaped Middle East since the retreat of traditional powers and the reduced involvement of the United States, forging ties with Israel and joining a war against Iran-backed militants in Yemen.

Sheikh Khalifa bin Zayed's death

Sheikh Mohamed's predecessor, Sheikh Khalifa Bin Zayed Al Nahyan, passed away on Friday.

The Ministry of Presidential Affairs announced the death of Khalifa, who was also ruler of the UAE's richest emirate, Abu Dhabi, but gave no details.

“The Ministry of Presidential Affairs mourns to the UAE people, Arab and Islamic nations and the world the death of President His Highness Sheikh Khalifa bin Zayed Al Nahyan, who passed away on Friday,” the ministry said in a statement on state media.

The UAE would observe a 40-day mourning period with flags flown at half-mast as of Friday and suspend work at all public and private sector entities for three days, the ministry added.

Condolences started pouring in from Arab leaders including Bahrain's king, Egypt's president and Iraq's prime minister soon after Khalifa's death.

In his condolence message, Prime Minister Shehbaz Sharif said he was deeply grieved to hear about Sheikh Khalifa bin Zayed's death.