UAE President "Sheikh Khalifa bin Zayed al-Nahayan" has undergone an operation after suffering a stroke and is in a stable condition, the presidential affairs ministry said on Saturday.
The ministry said in a statement carried by state news agency WAM that Sheikh Khalifa suffered a stroke on Friday "that led doctors to operate on him... He is in a stable condition".
He became president of the United Arab Emirates and ruler of the oil-rich emirate of Abu Dhabi in November 2004, when he succeeded his late father sheikh Zayed bin Sultan, who founded the federation in 1971.
Sheikh Khalifa, who turned 66 on Saturday, was just 21 when he was named Abu Dhabi's crown prince on February 1, 1969.
Abu Dhabi sits on the bulk of the UAE's oil wealth, ranked the world's seventh largest, which makes it the wealthiest of the seven UAE sheikhdoms.
In addition to Abu Dhabi, the UAE comprises the emirates of Ajman, Dubai, Fujairah, Ras al-Khaimah, Sharjah and Umm al-Qaiwain.
Sheikh Khalifa was re-elected head of the UAE for a second five-year term in 2009 by the Supreme Federal Council, the body that designates both the president and vice president of the Gulf state.
It comprises the rulers of the seven UAE emirates.
His brother, Sheikh Mohammad bin Zayed, succeeded him as crown prince. Sheikh Mohammad is also the deputy supreme commander of the UAE armed forces and chairman of the Abu Dhabi executive council.