The UK, France and Germany are to retain sanctions on Iran in an attempt to deter Tehran from selling drones and missiles to Russia.
Iran has said the move is illegal and provocative and clearly violated the terms of the nuclear deal.
In 2015 Iran agreed to a nuclear deal and, under the terms, some sanctions were due be lifted next month. However, the European nations believe Iran breached the deal by enriching and storing uranium.
The European powers announced that they would incorporate expiring UN sanctions into their own laws.
Some of the measures are supposed to stop Iran developing and exporting ballistic missiles and drones. But despite the sanctions, many drones made in Iran have been used by Russia in its war against Ukraine.
Iran agreed to the deal, known as the Joint Comprehensive Plan of Action (JCPOA), with a group of world powers known as the P5+1 – the US, UK, France, China, Russia and Germany – eight years ago.
Under the 2015 accord, Iran agreed to limit its sensitive nuclear activities and allow in international inspectors in return for the lifting of crippling economic sanctions. The accord bars anyone from buying, selling or transferring drones and missiles to and from Iran.
The agreement envisaged a transition day eight years later, when remaining ballistic missile and nuclear-related sanctions on Iran would be lifted.
The deal also included an asset freeze on a list of people and organisations believed to be helping advance the nuclear programme.
Countries such as Russia and China will no longer be bound by the restrictions if they do not adopt sanctions similar to those of the UK, France and Germany before 18 October.
The latter three countries, known collectively as the E3, said the sanctions would remain in place until Tehran was fully compliant with the deal.