President Obama shows support for South Korea
25 April 2014 Last updated at 14:23 BST
President Obama has been holding talks with South Korean leader Park Geun-hye as part of his tour of Asia.
His visit comes amid concerns North Korea could be planning to conduct a fourth nuclear test, following reports of activity at its nuclear test site.
Mr Obama said said America stood "shoulder to shoulder" with South Korea over North Korean provocation.
He also expressed his condolences over last week's ferry disaster.
Lucy Williamson reports from Seoul.