Image copyright Reuters Image caption South Korean forces have been holding exercises along the border with the North

US Secretary of State Rex Tillerson has insisted President Donald Trump wants to resolve the confrontation with North Korea through diplomacy.

It will continue until "the first bomb drops", he told CNN.

Sanctions and diplomacy, he said, had brought unprecedented international unity against North Korea's nuclear weapons programme.

Last month, Mr Trump told Mr Tillerson not to waste time seeking talks with Kim Jong-un.

Mr Tillerson's remarks come as the US and South Korea begin their latest joint military exercise in waters surrounding the Korean peninsula, involving fighter jets, destroyers and aircraft carriers.

The drills regularly anger the North, and Pyongyang has in the past denounced them as a "rehearsal for war".

Image copyright Reuters Image caption Rex Tillerson said Mr Trump wanted the issue "solved diplomatically"

In Sunday's interview, Mr Tillerson again refused to comment on whether he had referred to Mr Trump as a moron after a July meeting at the Pentagon.

"I'm not going to deal with that petty stuff," he replied, saying he would not dignify the question with an answer.

The president responded by challenging the secretary of state to an IQ test but a spokeswoman said later it had been a joke.

Lines of communication

In recent months, North Korea has defied international opinion by conducting its sixth nuclear test and launching two missiles over Japan.

Analysts say the secretive communist state is clearly set on developing a nuclear-capable missile, able to threaten the continental US, despite UN sanctions.

At the end of last month, Mr Tillerson disclosed that the US was in "direct contact" with the North and looking at the possibility of talks.

After months of heated rhetoric, it came as a surprise to some that the two countries had lines of communication.

However, the next day Mr Trump tweeted Mr Tillerson to say: "Save your energy Rex, we'll do what has to be done!"