United Arab Emirates (UAE) President Sheikh Khalifa bin Zayed Al Nahyan died on Friday, the government's state-run news agency announced in a brief statement.
In a statement, the ministry mourned for "the people of the UAE, the Arab and Islamic nation, and the whole world, the leader of the nation His Highness Sheikh Khalifa bin Zayed Al Nahyan," according to the official news agency (WAM).
The UAE's long-ailing ruler, also known as a pro-Western modernizer who had aligned the Gulf Arab state closer to the United States and its allies, passed away at the age of 73, WAM reported, after battling illness for several years.
He had long ceased having involvement in day-to-day affairs, with his brother, Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed Al Nahyan (MBZ), seen as the de-facto ruler. There was no immediate announcement about the successor.
The UAE's Ministry of Presidential Affairs announced a 40-day period of mourning and a three-day suspension of work in all ministries and the private sector beginning Friday, including flags to be flown at half-staff.
Born in 1948, Sheikh Khalifa was chosen in 2004 to succeed his long-serving father Sheikh Zayed bin Sultan Al Nahyan, who ascended the throne in 1971.
"The UAE has lost its righteous son and leader of the 'empowerment phase' and guardian of its blessed journey," MBZ said on Twitter, praising Khalifa's wisdom and generosity.
MBZ has for years been the de facto ruler of the UAE, an OPEC oil producer and a major trade and tourism hub that has moved to build its political influence in the region and abroad.
The crown prince is poised to become the new ruler of Abu Dhabi, which holds most of the UAE's oil wealth and has held the presidency since the founding of the UAE federation by Sheikh Khalifa's father, the late Sheikh Zayed, in 1971.
Under the constitution, Vice President and Prime Minister Sheikh Mohammed bin Rashid Al Maktoum, ruler of Dubai, would act as president until the federal supreme council, which groups the rulers of the seven emirates, meets within 30 days to elect a new president.
Diplomats and analysts expect MBZ to become the new president, further consolidating Abu Dhabi's power which had already grown under Sheikh Khalifa, who came to power in 2004.
This would come at a time when Abu Dhabi's ties with Washington have been visibly strained over perceived U.S. disengagement from its Gulf allies' security concerns.
"Not much will change in UAE foreign & domestic policies, except MBZ will have even less reason to seek consensus w/Dubai & other Emirates," tweeted Cinzia Bianco, a research fellow at European Council on Foreign Relations.
MBZ led a realignment of the Middle East that created a new anti-Iran axis with Israel and fought a rising tide of political Islam around the region.
Condolences started pouring in from Arab leaders, the United States and from Israel, with which the UAE forged ties in 2020 alongside Bahrain.
"Sheikh Khalifa's bold leadership contributed so much to the advancement of the UAE and its people and to the growing partnership between our countries and is a great legacy for his successors," said Israeli President Isaac Herzog.
The U.S. mission to the UAE said Sheikh Khalifa was "a true friend of the United States."
At home, Emiratis remembered Sheikh Khalifa for his generosity and his push to develop the UAE, which has a population of some 10 million, the majority expatriate workers.
"The people of the UAE are thankful to the president for the opportunities he had created them, for the development of the country under his leadership," Emirati citizen Ali al-Khatri, 32, told Reuters in the capital Abu Dhabi.