"We are worried about what's happening in Iran. I'm disappointed at the failure of Iran to accept the dialogue and we now need to look again at what needs to happen there," Catherine Ashton told Sky News in an interview.
"The next step for us is to take our discussions into the Security Council. When I was meeting with (US Secretary of State) Hillary Clinton last week we talked about Iran and we were very clear this is a problem we will have to deal with," she said.
"We need to now look at the most effective way of doing so."
Clinton, speaking in London last week, said the international community was moving toward consensus on imposing new sanctions on Iran over its nuclear ambitions.
The United States and its major European allies are keen to tighten sanctions but Russia and China, which both have important commercial ties to Iran and hold veto rights on the Security Council, are more reluctant.
Tehran says its only goal is generating nuclear energy, but Washington accuses it of trying to develop nuclear weapons.