各国领导人齐聚核安全峰会

This is Barack Obama charm offensive of work, 46 countries, 36 world leaders, and the US president appealing for their help. The words whispered in their ears of the family photo, the pressure applied on the issue. The US believes it's one of the biggest threats to global security. And Obama believes many of these world leaders don't take it seriously enough.

It's estimated there is enough so called loose nuclear material floating around the globe to make 120,000 unclear weapons in all military bases, power stations, universities. And the US believes not enough is being done to make it secure. It worries Washington enough to convene the biggest summit  the US has seen since 1945. And Obama opened the meeting with a warning for the world.

"Two decades after the end of the Cold War. We face a cruel irony of history. The risk of a nuclear confrontation between nations has gone down, but the risk of nuclear attack has gone up."

Among those not at the summit, Iran, its pursuit of nuclear technology whether peaceful or not is not even on the agenda officially, but Obama is gently pushing world leaders to back tough action against Teheran. He spent 90 minutes talking to President Hu of China, and believes he is winning Beijing's support for a new Security Council resolution whether that extends to more sanctions isn't so clear. This summit has already delivered some of what Obama wants but they are small steps. Countries like Ukraine and Canada, agreeing to hand over nuclear waste. If he is to make progress on the bigger goals, he needs to keep making friends.