Obama says North Korea nuclear programme is serious mid-term risk

US President Barack Obama said on Thursday that North Korea's nuclear ambitions pose a serious medium-term threat, adding that engagement with China and other countries had seen progress on the issue.

"It's something that we've put at the centre of discussions and negotiations with China," Obama told reporters.

"What we've seen is improved responses from China and countries in the region...that may reduce the risks of North Korea selling weapons or missile material to other countries."

Obama was speaking on the first day of a two-day Group of Seven summit in Ise-Shima, central Japan. He said leaders from the G7 summit had discussed the need to sustain economic growth in the United States, adding that progress was starting to emerge in Europe's economy.