The government of Iran has threatened to seize a British ship after her oil tanker was intercepted by Royal Marines off Gibraltar for trying to take oil to Syria in violation of European Union (EU) sanctions.

A spokesman for the Gibraltar government said the 28-strong crew of the Iranian oil tanker are being interviewed as witnesses and not criminals.

The spokesman said the crew, who have remained on board the super tanker were mainly Indians, with some Pakistanis and Ukrainians.

Police and customs officials remained on board the vessel to carry out their investigations.  This is even as Gibraltar’s Supreme Court has granted a 14-day extension for authorities to detain the tanker.

EU sanctions against the Syrian government took effect in May 2011 shortly after the start of President Bashar al- Assad’s bloody crackdown on pro-democracy demonstrators.

Iran, a close ally of Assad is also under a US sanctions regime meant to bar all international sales of Iranian oil. The sanctions were imposed after President Donald Trump withdrew Washington from a nuclear deal with Tehran last year.