Donald Trump has vowed to protect South Korea against the "instability in North Korea".
The US President-elect had a call with South Korean President Park Geun-hye last night, her office said. She congratulated him on his election victory and said she hoped the ties between the two countries would grow further over his presidency.
Trump allegedly said: "We will be steadfast and strong with respect to working with you to protect against the instability in North Korea."
Guen-hye also asked Trump to join the effort against North Korea's leadership and use deterrence against the capital. She also invited him to visit the country.
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During the election campaign Trump said he would consider withdrawing some of the 28,500 troops stationed in the country unless Seoul paid a greater share of the costs. He claimed they were paying them "peanuts" but this year it is estimated that they would pay around half the cost. If they were to withdraw, the case for developing nuclear weapons to protect against the North could grow.
He has also said that war between the North and South would be a "terrible thing" but implied that they would be on their own, with no US support. "If they do, good luck. Enjoy yourself, folks."
Trump said North Korean leader, Kim Jong-un, was "a maniac" and "doesn't play games".
Many countries in the far-east are concerned at Trump's promises to slap 45 per cent tariffs on foreign imports from countries such as China.
But the warning shots have been fired. An article in China's state-run Global Times states: "If Trump wants to target bilateral trade, he should first weigh the consequences of China's countermeasures."