Obama in S Korea amid nuclear fears

US President Barack Obama is in Seoul for a visit that comes amid concern that North Korea may be planning a fourth nuclear test. Mr Obama, who arrived from Japan on the second stop of his Asian tour, has held talks with South Korean leader Park Geun-hye. Their talks were set to focus on North Korea, following reports of activity at the Punggye-ri nuclear test site. Ahead of the talks, Mr Obama expressed grief over last week\'s ferry disaster. More than 300 people were killed or remain missing after the Sewol passenger ferry sank off South Korea, in a tragedy that has shocked the nation. Most of those who died were teenagers on a school trip, according to BBC.