Iran the world s "biggest state sponsor of terrorism"

S Defence Secretary James Mattis has called Iran the world s "biggest state sponsor of terrorism", amid rising tensions between the two nations.

His comments come a day after the Trump administration imposed new sanctions against Iran in response to a ballistic missile test.

But Mr Mattis said he did not see any need to boost US troop numbers in the Middle East to deal with Iran.

Iran has been carrying out military exercises in a show of defiance.

Tense but unclear Trump-Iran relations

The Revolutionary Guards, set up to defend Iran s Islamic government, said the drills would "showcase the power of Iran s revolution and to dismiss the sanctions".

Iranian-built missile systems, radars, command and control centres, and cyber warfare systems are being tested during Saturday s exercises, state media reported.

A senior commander said the armed forces were ready to "rain down missiles" on the country s enemies if attacked.

"We are working day and night for the security of the Iranian nation," said Amir Ali Hajizadeh, the commander of the Revolutionary Guards air force.

Playing with fire

US officials said the sanctions, targeting 13 people and 12 companies, were in response to last Sunday s missile test and what they called Iran s "continued support for terrorism".

They are the first Iran sanctions of Donald Trump s new presidency, who has signalled a tougher stance on Iran than the Obama administration.