THE US Secretary of State Rex Tillerson has warned that a pre-emptive strike against North Korea might be necessary if the threat from its weapons programme reaches a level “we believe requires action”.

Tillerson was speaking in Seoul, in South Korea, after visiting the heavily militarised border with the North.

Asked about the possible use of military force against the North, Tillerson replied: “All of the options are on the table.”

He said Washington did not want a military conflict, but cautioned that if Pyongyang took actions that threatened South Korean or US forces, it would be met with an “appropriate response”.

Previous US administrations have considered military force because of North Korea’s development of nuclear missiles, but rarely has the option been expressed quite so explicitly.

Earlier, Tillerson had landed by a helicopter at Camp Bonifas, an American base near the demilitarised zone created after the Korean War effectively ended in 1953.

He is the latest senior US official to have their pictures taken at the border, but it is the first trip by the new Trump administration’s senior diplomat. He is touring Japan, South Korea and China.

Speaking in Tokyo, Tillerson had vowed a tougher strategy to confront North Korea’s nuclear threat, but he offered no details about what would comprise the “different approach”. He did note that 20 years of “diplomatic and other efforts” had failed to dissuade the isolated communist government from developing its nuclear programme, which he called an “ever-escalating threat”.

Meanwhile, Donald Trump has stood by his unproven claim that his predecessor Barack Obama wiretapped his phones.

The US President suggested he was the victim of the same sort of surveillance the Obama adminis- tration was once alleged to have used to monitor German Chancellor Angela Merkel’s calls.

“At least we have something in common, perhaps,” Trump said during a joint news conference with Merkel.

Trump’s allegations against Obama have sparked reactions ranging from bafflement to anger in Washington, with both Democrats and Republican lawmakers saying they have no evidence to support his claim.

But the White House’s refusal to back down has created more problems for the new administration.

On Thursday, spokesman Sean Spicer defended the president’s comments by repeating a Fox News analyst’s report that GCHQ, the British electronic intelligence agency, had helped Obama wiretap Trump.

The agency vigorously denied the charge and Britain’s ambassador to Washington, Kim Darroch, complained directly to White House officials.

Trump tried to distance himself from the report on Friday.

“All we did was quote a certain very talented legal mind who was the one responsible for saying that on television,” Trump said, referring to analyst Andrew Napolitano. “You shouldn’t be talking to me, you should be talking to Fox.”

The British government said the White House has promised it will not repeat the allegation. Spicer, speaking with reporters following Trump’s news conference with the German Chancellor, said: “I don’t think we regret anything.”

Trump tweeted earlier this month that Obama “was tapping my phones in October” and compared the incident to “Nixon/Watergate” and “McCarthyism”.

The claim is prompting growing bipartisan agreement that there is no evidence to back up the claim and mounting pressure to retract the statement.

The Senate Select Committee on Intelligence weighed in on Thursday, finding “no indications” that Trump Tower was the subject of surveillance.

Republicans in Congress also said Trump should retract his claims. Chairman of the House Select Committee Charlie Dent called the accusation against Britain “inexplicable” and the accusation against Obama unfounded.