British Prime Minister Gordon Brown said Tuesday that Iran must come into the international fold or face isolation, ahead of "crucial" talks on its nuclear programme in Geneva this week.
In a keynote speech to his ruling Labour Party's annual conference, he also pledged continued support to US President Barack Obama in Afghanistan "to make sure that terrorism doesn't come to the streets of Britain."
The five UN Security Council permanent members -- the United States, Russia, China, Britain and France -- plus Germany are due to take part in talks with Iran's top nuclear negotiator, Saeed Jalili, on Thursday.
"I say to Iran as they face a crucial date this week; join the international community now or face isolation," Brown told his party in the resort of Brighton on England's south coast.
The United States, the European Union and Israel fear that Iran is secretly developing nuclear weapons under the guise of its civilian nuclear power programme, but Tehran denies the charges and says the programme is peaceful.
On Afghanistan, Brown said: "Britain will work with President Obama and 40 other countries for peace and stability for the people of Afghanistan, and to make sure that terrorism doesn't come to the streets of Britain."
Under his predecessor Tony Blair, Britain was controversially the United States' main ally in military action in Afghanistan and Iraq following the September 11, 2001 attacks.
British forces were withdrawn from Iraq this summer, but public criticism of Britain's involvement in Afghanistan has been fuelled by a surge in military deaths there in recent months.