British Foreign Secretary David Miliband warned Iran on Thursday that it must cooperate with international talks in Geneva about its nuclear program.
Miliband told an annual conference of Britain's governing Labour Party that discussions involving Iran, the US and five other world powers are vital to hopes of persuading Tehran to freeze its nuclear activities.
The US and allies accuse Iran of attempting to develop a nuclear weapon. Teheran rejects the claim, and insists it is constructing a civilian power program.
"Our message to Iran is simple: do not mistake respect for weakness," Miliband said, speaking in Brighton, southern England.
"After 16 months of prevarication, they need to get serious. Over the next few months, the stakes could not be higher - the Arab world on tenterhooks, Israel on alert," Miliband told delegates.
Britain has sent a senior diplomat, Mark Lyall Grant, to the Geneva talks.