Vice President Joe Biden underlined the United States' willingness to talk directly with Iran, but only so long as that government is willing to work toward a specific goal.
Biden said the Obama administration would not sit down with Iran "just for exercise," placing the onus on the Iranian government to make a show of good faith.
"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 told an international security conference in Munich.
"There is still time, there is still space for diplomacy backed by pressure to succeed," he added.
Iran is expected to meet with the five permanent members of the U.N. Security Council, as well as Germany, in the near future. But so far, efforts to diplomatically strike an agreement on Iran's development plans have made little headway.
Biden insisted the U.S. was willing to sit down with Iran, provided that government showed it was serious. He offered no timeline for when such talks could occur, but said it could happen "when the Iranian leadership, the supreme leader [Ayatollah Ali Khameni] is serious."
"That offer stands, but it must be real and tangible and there has to be an agenda that they're prepared to speak to," he added.
Biden's remarks came as the U.S. continues to apply mounting economic sanctions on Iran. The vice president emphasized that America's overarching goal is preventing Iran from acquiring a nuclear weapon, and that it is up to the Iranian government to remove those sanctions.
"Iran's leaders need not sentence their people to economic deprivation and international isolation," he said.