Continuing his tour of Asia, President Obama has arrived in South Korea – warning the North not to conduct another nuclear test.

The US leader’s trip comes amid reports of increased activity at a nuclear site in the North.

Seoul says the intelligence suggests Pyongyang may be planning a fourth test.

Obama began his visit at the National War Memorial, paying tribute to soldiers from the South who died in the Korean War of 1950-53.

Earlier, in Japan, Obama called on China to dissuade its neighbour from continuing its nuclear programme.

There are fears that North Korea may look to disrupt the US president’s visit with a show of strength.

Pyongyang is persistently irritated by joint US-South Korean military co-operation.

But it is also thought that the likelihood of irking Beijing – North Korea’s only major economic prop – may deter it from actually carrying out a nuclear test.

Obama’s visit comes as South Korea is preoccupied with the Sewol ferry tragedy in which hundreds of children died.