
"The United States will be steadfast and strong with respect to working with the ROK to protect against the instability in North Korea," Trump told South Korean President Park Geun Hye in a telephone call, according to a statement issued by the president's office in Seoul Thursday.
"We are with you all the way and we will not waver," Trump was quoted as saying.
Park stressed that North Korea's nuclear programme was the biggest threat currently facing South Korea and the US.
Observers fear that the South Korean government might face lengthy negotiations with a Trump administration over how the costs of some 28,500 US soldiers stationed in South Korea are financed.
During his campaign, Trump had called for US allies to pay a stronger share of such defence costs.