The US is ready to hold talks with Iran on its disputed nuclear programme but not just "for the exercise," US Vice President Joe Biden said Saturday.
"We would be prepared to meet bilaterally with the Iranian leadership... that offer stands but it must be real and tangible," he told the Munich Security Conference.
"There has to be an agenda that they are prepared to speak to. We're not just prepared to do it for the exercise," he added, speaking on the second day of the annual three-day gathering in southern Germany.
Kicking off his three-nation European tour that will also take in Paris and London, Biden warned Iran in a German newspaper interview Friday that opportunities for diplomacy were not unlimited but offered direct talks between Washington and Tehran.
"There is still time, there is still space for diplomacy, backed by pressure, to succeed," Biden told participants in Munich.
"The ball is in the government of Iran's court and it's well past time for Tehran to adopt a serious good faith approach to negotiations," he added.
Iran and six world powers -- the US, China, Russia, Britain, France and Germany -- held three rounds of talks last year aimed at easing the standoff over Iran's nuclear activities.
The six, known as the P5+1, called on Iran to scale back its programme but stopped short of meeting Tehran's demands to reduce sanctions. The last round ended in stalemate in June in Moscow.
Russian Foreign Minister Sergei Lavrov said here that "mistrust" must be overcome and that Iran needed to be convinced it was "not about regime change."