"We are going to adopt a very vigorous approach, a very intensive approach to try to complete our work," IAEA director general Mohamed ElBaradei told reporters.
He was speaking after the IAEA told Iran to prove by October 31 that it is not trying to secretly develop nuclear weapons, as Washington accuses it of doing.
ElBaradei said the IAEA ultimatum was "sending a very powerful message to Iran that they need to cooperate fully and immediately and to show complete transparency".
"We also need the support of other countries who have been supporting the Iran (nuclear) program," ElBaradei said.
The IAEA needed to make sure it obtained "all the information we need", he added.
Asked about Iranian threats to cut off cooperation with the IAEA because of the ultimatum, ElBaradei said: "I think they will get over that. I think they will understand it is in their interest to cooperate with us."
"I need them to be pro-active, I need them to be transparent," ElBaradei said.
"We are not going to duck any issue but we are not going to jump to any conclusions," he said.