Iran has no right to spark a nuclear arms race in the Middle East, the UK's foreign secretary has warned.
David Miliband was promoted by new PM Gordon Brown
David Miliband told the Financial Times the global community must remain "clear and united" in pursuing a diplomatic solution to Tehran's nuclear ambitions.
He also warned Russia not to refuse to extradite suspects in the Alexander Litvinenko murder case.
Mr Miliband succeeded Margaret Beckett at the Foreign Office 10 days ago as part of PM Gordon Brown's reshuffle.
Iran has been accused of not co-operating with the UN over its nuclear programme, amid fears it is enriching uranium to use in weapons.
Mr Miliband said the West was making a "very clear offer" to allow Tehran to develop non-military nuclear power, but said the country "doesn't have the right to undermine the stability of its neighbours".
UK-Iranian relations were tested earlier this year when a group of Royal Navy personnel was held captive by Tehran, accused of illegally entering its waters.
In the newspaper interview, he also dealt with issues surrounding Iraq and Afghanistan, where British troops have been fighting for several years.
On Iraq, he followed the lead of his predecessors saying: "As Iraqi capacity is built up, we hand over to Iraqi control."
Dealing with calls from anti-war groups for an independent inquiry into the conflict, he said his "first priority" should be the "safety of our troops".
"I think we can look at questions of inquiries later, but that's not where I'm spending my time in my first week," he said.
On Afghanistan, where British troops have been engaged since 2001, he told the paper that the UK has the resources, ideas and the people to win the conflict.
UK-Russian relations have been strained since last November, when ex-spy Mr Litvinenko died of radiation poisoning in London.
Earlier this week, Russian officials rejected an extradition request for Andrei Lugovoi, the prime suspect in the murder.
Mr Miliband said a refusal by Russia to extradite suspects would be treated "with the seriousness it deserves".
More generally, he hinted at a continuation of the interventionist style of foreign policy promoted by former Prime Minister Tony Blair.
"Britain must not retreat from the world," he said.
The country has the opportunity to be a "global hub" economically and politically, he added.
Mr Miliband was promoted by Mr Brown from the environment department.
At the age of 41, he is among the youngest politicians to serve as foreign secretary.