Presumptive US Republican presidential candidate Donald Trump has admitted he "has regrets" about his US election campaign but said he would not have been successful otherwise.

He was speaking to Fox News presenter Megyn Kelly, with whom he has had a feud since a TV debate last August.

When pressed about why he re-tweeted "bimbo" jibes about her, he said: "Did I say that? Ooh. Excuse me."

In another interview, he said he was open to meeting North Korea's leader.

The interview with Ms Kelly was largely seen as an attempt to bury the hatchet after months of rancour between the two, with the journalist taking the initiative to set it up.

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During the August debate, Ms Kelly had probed Mr Trump on his comments about women.

Afterwards, he insinuated she had treated him unfairly because she was menstruating.

"You could see there was blood coming out of her eyes, blood coming out of her - wherever," he said.

In March, Fox defended Ms Kelly, saying: "Donald Trump's vitriolic attacks against Megyn Kelly and his extreme, sick obsession with her is beneath the dignity of a presidential candidate who wants to occupy the highest office in the land."

Ms Kelly revisited the issue on Tuesday night, as well as asking Mr Trump whether he regretted certain comments about Senator John McCain and former rival for the Republican nomination Carly Fiorina.

Image copyright Fox Image caption Fox News presenter Megyn Kelly challenged Mr Trump for calling her a bimbo

He said: "I guess so, but you have to go forward. You can correct a mistake, but to look back and say 'I wish I didn't do this or that', I don't think that's good, I don't think that's healthy."

He added: "When I'm wounded. I go after people hard and I try and un-wound myself."

Mr Trump said he did "pretty well with real tweets" but that "the re-tweet is really more of a killer", adding he "could have done without'' his re-tweet of a post mocking the appearance of Heidi Cruz, wife of former campaign rival, Ted Cruz.

While Mr Trump asked to be excused about the bimbo re-tweets, he also told Ms Kelly she must have been "called a lot worse".

Ms Kelly also asked if Mr Trump had any regrets about his nine-month campaign.

He said: "Absolutely, I have regrets... I could have done certain things differently, I could have maybe used different language but overall I have to be very happy with the outcome."

He would not specify what the regrets were.

He added: "If I didn't conduct myself in the way I've done, I don't think I would have been successful."

Mr Trump also said that if his campaign to win the presidency ended in failure then "I will consider it to be a total and complete waste of time, energy and money".

'Bizarre fascination'

In an interview with Reuters news agency late on Tuesday, Mr Trump said he would be willing to meet North Korea's leader to discuss its nuclear programme.

Media playback is unsupported on your device Media caption Donald Trump: "China can solve that problem with one meeting or phone call"

"I would speak to him, I would have no problem speaking to him," the businessman said of Kim Jong-un.

Such a meeting would mark a significant change of US policy towards the politically isolated regime.

Democratic front-runner Hillary Clinton decried Mr Trump's "bizarre fascination with foreign strongmen".

Mr Trump has also previously said he respects Russian President Vladimir Putin, although on Tuesday he expressed disapproval of Mr Putin's military actions in eastern Ukraine.

On the subject of North Korea, the New York property developer said he would pursue face-to-face talks and added that he would also put pressure on China, as North Korea's only major ally.

Trump follows Obama? BBC's Stephen Evans in Seoul

The South Korean media hang on Mr Trump's every word - but don't then fly into spasms of high emotion. They cover the quotes - colourful as they are - but generally don't react beyond reportage. Politicians, too, are observing but not speaking. "Bemusement" might be the best way to describe the reaction.

After all, Barack Obama said before he was first elected, that he too would be prepared to meet the North Korean leader of the time [Kim Jong-un's father, Kim Jong-il] face-to-face.

It's true that Mr Obama's promise was nine years ago and North Korea was not so far down the path to getting a nuclear arsenal. And Mr Trump has not been so cool in his language.

He recently called Kim Jong-un a "maniac" but then added what sounded like a compliment at the way the North Korean leader had consolidated his power: "How many young guys - he was like 26 or 25 when his father died - take over these tough generals, and all of a sudden... he goes in, he takes over, and he's the boss.

"It's incredible. He wiped out the uncle, he wiped out this one, that one. I mean this guy doesn't play games. And we can't play games with him."

Read more from Stephen

Following Mr Trump's comments, South Korea's Yonhap news agency quoted China's foreign ministry spokesman Hong Lei as saying that Beijing "supports direct dialogue and communication between the US and North Korea", adding: "We think this is a very conducive thing to do."

North Korea first tested nuclear weapons in 2006, in breach of international agreements, and has made repeated threats of nuclear strikes against South Korea and the US.

The US and North Korea have no formal diplomatic relations.

Mr Trump won the Republican primary in Oregon on Tuesday, where Bernie Sanders emerged victorious in the Democratic race.

The Kentucky primary, which was Democratic-only, was too close to call but Hillary Clinton declared victory with most of the votes counted.