Vice-President Biden is underlining the strength of US ties with Europe
US Vice-President Joe Biden has warned that Iran's actions risk sparking a nuclear arms race in the Middle East.
His warning came in a speech to the European Parliament - the first by a top US leader since then-president Ronald Reagan spoke there in 1985.
Iran's leaders "spurn our collective good faith efforts", Mr Biden said, and risk "continuing isolation".
Iran insists it has the right to develop civil nuclear power. The US suspects it of seeking atomic weapons.
"Wouldn't it be ironic as the Iron Curtain fell... that a new arms race would emerge in some of the most unstable parts of the world," Mr Biden said.
"That would be an irony that our children, our grandchildren and our great-grandchildren would not forgive us, in my view, to allow to come to pass," he added.
Pressure on Iran
Mr Biden's warning echoed the words of US Secretary of State Hillary Clinton, who told delegates at a nuclear Non-Proliferation Treaty (NPT) conference this week that Iran had violated its obligations and should be held to account.
Earlier, President Mahmoud Ahmadinejad of Iran accused states with nuclear weapons of threatening those who wanted to develop peaceful nuclear technology.
His comments prompted delegates from the US, the UK and France to walk out.
The US is negotiating with other Security Council members to impose a fourth round of UN economic sanctions against Iran over its uranium enrichment programme.
A listening administration
Mr Biden told MEPs in Brussels on Thursday that "we are back in the business of listening to our allies".
"It's no accident that Europe is my first overseas destination as vice-president. We need each other more now than we have ever."
He welcomed the new powers acquired by the European Parliament under the EU's Lisbon Treaty, saying "the Obama-Biden administration strongly supports a vibrant EU".
He stressed that a strong EU was "absolutely essential to American... long-term security".
On the dispute over EU personal data transfers to the US as part of anti-terrorism measures, he warned that "the longer we are without agreement the greater the risk".
"The terrorist finance tracking programme is essential to our security," he said, but added: "I understand your concerns".