Donald Trump’s national security adviser yesterday warned Russia there would be no deal on Syria unless Iranian troops withdrew from the country.

The US and Israel have been pressuring Moscow over the matter of Iran’s presence in Syria, where thousands of Iranians are fighting in support of the Bashar al-Assad regime.

However, yesterday’s comments from John Bolton marked the first time Washington had issued such a direct ultimatum.

"We're going to see what we and others can agree in terms of resolving the conflict in Syria,” Mr Bolton, who is known to be a hawk on foreign policy, told reporters during a visit to Israel. “But the one prerequisite there is the withdrawal of all Iranian forces back in Iran."