PRIME Minister Julia Gillard expressed solidarity with South Korea in the face of nuclear threats from the north before heading to China for talks. As Ms Gillard left Australia on Friday, the prime minister said she had spoken to President Park Geun-hye on Thursday to express Australia's concerns over the serious risk to regional security posed by North Korea's threats of a nuclear strike. In their phone call, Ms Gillard emphasised the importance Australia placed on South Korea's security and promised to continue pressuring the rogue state to put an end to its stance and engage in dialogue with the south. Ms Gillard is due to arrive in China for a six-day visit on Friday evening, as tensions continue to mount over the warlike rhetoric coming out of North Korea. With her is Foreign Minister Bob Carr, who has said he will make a personal appeal for China to persuade North Korea to "ratchet down" its behaviour. In Canberra on Friday, US ambassador Jeffrey Bleich said there would be no changes to the American military presence in Australia following the North Korean threats. But he did say the US was taking the threats seriously in all its missions around the world. "We're not aware of any capability by North Korea, even with weapons they've identified ... being able to conduct a strike in Australia," he told AAP. From that perspective, no, we haven't changed our posture here. Mr Bleich said the US had been very clear with China about its views, given China's special relationship with North Korea. "It's incumbent on (China) to express concerns of all us about the belligerence of North Korea," he said. I know the prime minister is committed to reinforcing that message.