A group of six world powers has called on Iran to enter talks on its controversial nuclear program without preconditions.

At a board meeting of the U.N.'s nuclear watchdog in Vienna on Thursday, the group known as the P5+1 said that the process should be a “serious dialogue” that produces “concrete results.” The West fears Iran is developing nuclear weapons. Iran says its nuclear ambitions are peaceful.

The world powers group includes the five permanent members of the U.N. Security Council – the United States, China, Russia, France and Britain – plus Germany.

The statement reaffirmed support for a diplomatic solution. It also urged Iran to grant International Atomic Energy Agency inspectors access to its Parchin facility, which has been closed to them.

Also Thursday, Iran's Supreme Leader Ayatollah Ali Khamenei said he welcomes U.S. President Barack Obama's statements earlier this week that there is still time to address the nuclear issue diplomatically.

Israel believes a nuclear-armed Iran would be a threat to its existence and has warned it may take military action to stop Iranian nuclear activities.

Nuclear experts accredited to the IAEA have identified Parchin as the location of suspected nuclear-weapons-related testing.

Iran denies allegations it is attempting to develop atomic weapons and says its nuclear activities are only to generate power or for research purposes.