Obama’s nuclear summit

Leaders and delegates from 47 countries have begun arriving in Washington for what US officials say is an unprecedented summit on nuclear security.

The Obama administration has said the meeting is aimed at confronting the threat of nuclear terrorism, as well as how to safeguard loose nuclear weapons and material.

Iran and North Korea have not been invited to attend the two days of talks.

Al Jazeera’s Patty Culhane reports from Washington.