The United States denies any involvement in a bomb blast that killed an Iranian scientist.
Turkey says that it has reached an in-principle deal with the United States to give support to some elements of Syrian opposition. Over a million Syrian refugees live in Turkish territory, including many Syrian opposition figures.
President of the United States Barack Obama opening the biggest international meeting hosted by the US since 1945, greets leaders from nearly 50 countries. World leaders at the summit hear dire warnings of the danger of nuclear material falling into the wrong hands.