Donald Trump has announced plans to develop a “state of the art” missile system to protect the US against attacks from Iran and North Korea.

Within minutes of becoming President, the Republican billionaire unveiled a policy to “rebuild the American military” by expanding the size of the armed forces.

Under a plan entitled ‘Making our military strong again’, President Trump said he would plough more money into the army, navy and air force.

He declared that American military dominance “must be unquestioned” and warned about the prospect of America's rivals leapfrogging the US on defence.

US president Donald Trump vows to put America first

Included in the 350-word document - posted on the White House website – is a pledge to “develop a state-of-the-art missile defense system to protect against missile-based attacks from states like Iran and North Korea”.

But the statement is light on detail and does not say whether the system would be different from missile defences that are already under development, such as the Patriot system.

It also fails to detail how much it would cost or how it would be paid for.

Mr Trump has also vowed to make tackling cyber warfare a “priority” and to improve veteran care.

Hacking dominated the US election campaign and the days following 8 November, when allegations swirled that the Russian government had interfered in the vote.

And he said “corrupt and incompetent” officials working at the Department of Veterans Affairs would be sacked.