The chief of the International Atomic Energy Agency says it has “done as much as it can do” to resolve the nuclear problem in Iran.

IAEA Director Mohamed ElBaradei added that the restoration of trust between the U.S. and Iran and the resumption of direct dialogue between the two are long overdue and important to settling the nuclear problem.

In an interview at this year’s World Economic Forum in Davos, he told U.S. magazine Newsweek that the political conflict between the U.S. and Iran has made it difficult to resolve the issue.

Defending himself from criticism that he has not been tough enough on Syria and North Korea for their pursuit of nuclear programs, ElBaradei said that at no point did he have the evidence that would have been required to make a definitive conclusion on the nature of the two nations’ activities.