US National Security Advisor John Bolton vowed on Tuesday to "squeeze" Iran "until the pips squeak", a week after a tough new round of sanctions came into force. Speaking in Singapore ahead of a summit, Bolton said: "We think the government is under real pressure and it's our intention to squeeze them very hard. As the British say, squeeze them until the pips squeak. We are also going to significantly increase the enforcement of sanctions."

The US measures have been opposed by other parties to the deal aimed at ending Iran's nuclear drive - Britain, Germany, China and Russia - who have vowed to keep the accord alive. UN inspectors say Iran is abiding by the deal.