John Kerry, the US secretary of state, has arrived in South Korea as tension with its northern neighbour continues.
Kerry's three-day visit, which began on Friday, will also take him to China and Tokyo.
The trip comes as Washington tries to press China to deliver a "tough" message to North Korea to rein in its nuclear programme and belligerent rhetoric, a US official said.
Al Jazeera's Marga Ortigas reports.
