Rice, on her first overseas trip since taking office, aims to heal trans-Atlantic ties damaged over Iraq and to start a new US peace effort in the Middle East, but Iran is an area of possible tension.
When asked on Friday whether she could envisage circumstances under which the United States would attack Iran, Rice said: "The question is simply not on the agenda at this point; we have diplomatic means to do this."
Britain and its EU partners Germany and France have been pursuing diplomacy with Tehran, which has agreed to suspend some of its nuclear activities while talks are ongoing.
Rice has said Iran, branded by Washington as part of an "axis of evil" with pre-war Iraq and North Korea, needs to live up to its obligations and agree to verification inspections.
She was critical of Iranian policies and what she called a lack of a democratic government but said diplomacy would take precedence.
Rice (R) met with Blair for talks
on Iraq and the Middle East
"I find that there is really very little difference between us about the challenges we face in dealing with the Iranian regime. We have many diplomatic tools still at our disposal and we intend to pursue them fully," she added.
Iran denies it is developing a nuclear bomb.
Rice earlier on Friday had talks with British Prime Minister Tony Blair on the first leg of a week-long tour of Europe, Israel and the Middle East.
Ahead of her forthcoming visit to the Middle East, Rice said the Palestinian leadership should take a decision to unite Palestinian security forces, Aljazeera learned.
Rice is scheduled to hold talks with Palestinian President Mahmud Abbas and Israeli Prime Minister Ariel Sharon during a visit to the region on Sunday and Monday.
Rice is due to meet Palestinian
President Abbas (R)
"There is now a process that is moving and moving effectively," Rice said about efforts to achieve Middle East peace.
"We have lots of work to do, especially as we try to bring Israelis and Palestinians the chance of a permanent peace."
Rice urged the international community to resume financial assistance to support Palestinian reforms.