Jerusalem (AFP) - Iran is still seeking to achieve nuclear military capabilities, Israeli Prime Minister Benjamin Netanyahu said Saturday, after a deal with world powers scaling down Tehran's nuclear abilities was implemented.

"Even after signing the nuclear deal, Iran has not relinquished its ambition to obtain nuclear weapons, and continues to act to destabilise the Middle East and spread terror throughout the world while violating its international commitments," a statement from Netanyahu's office read.

The premier said Israel would "follow the implementation of the deal and warn of any violation."

The historic nuclear accord between Iran and major powers entered into force Saturday as the UN confirmed that Tehran has shrunk its atomic programme and as painful sanctions were due to be lifted on the Islamic republic.

Israel, the Middle East's sole but undeclared nuclear power, tried to prevent the accord, arguing it would not stop Tehran from developing an atomic weapon if it wished.

Iran has always denied seeking a nuclear bomb.

"The world powers and (the UN atomic watchdog) must closely follow the activities at Iran's nuclear sites and other sites to ensure it is not continuing to clandestinely develop nuclear weapons," Netanyahu said.

"Without an appropriate reaction to every violation, Iran will realise it can continue to develop nuclear weapons, destabilise the region and spread terror."