Construction of the first of four reactors at the $20 billion Barakah plant has been completed ahead of "operation by the end of 2019 (or) early 2020," said the Emirates Nuclear Energy Corpation.
The first reactor had been due to come online last year, but the launch was initially delayed until 2018 to make time for regulatory approvals and complete safety checks.
No reason was immediately given for the latest postponement. But the International Atomic Energy Inspection Agency said on Sunday that it identified areas that need further action before the Barakah plant becomes operational.
State-owned ENEC said a second reactor was 93 percent complete, a third is 83 percent finished and the fourth was 72 percent complete.
The nuclear plant west of Abu Dhabi is being built by a consortium led by the Korea Electric Power Corporation.
When fully operational, the four reactors should produce 5,600 megawatts of electricity, around 25 percent of the UAE's needs, according to the energy ministry.
Nuclear and renewables are targeted to contribute around 27 percent of the UAE's electricity by 2021.
The UAE says it wants 50 percent of its energy to be generated by clean sources by 2050.
Saudi Arabia, the world's top crude oil exporter, plans to build up to 16 nuclear reactors, but the projects have yet to materialise.
In March, the kingdom said it would pursue nuclear weapons if its arch-rival Iran does. The comments drew alarm over a potential nuclear arms race in the Middle East.
Atomic experts say Israel remains the only country in the Middle East with a nuclear weapons programme. Former US president Jimmy Carter estimated in 2014 that Israel has more than 300 nuclear weapons.
Agencies contributed to this report.
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