Britain, France and Germany on Tuesday said they "deeply regret" Iran's decision to restrict site inspections by the UN's nuclear watchdog after a US refusal to lift existing sanctions.

The three European signatories to the 2015 nuclear deal with Iran said they were "united in underlining the dangerous nature of this decision".

"It will significantly constrain the (International Atomic Energy Agency's) access to sites and to safeguards-relevant information," they added.