Barak's remarks follow an earlier announcement by a US spokesman suggesting that Washington will not be seeking crippling sanctions against Tehran.
The US intends to pressure the Iranian government to change course on its nuclear program while protecting ordinary people, a US Administration spokesman said.
"It is not our intent to have crippling sanctions that have ... a significant impact on the Iranian people," State Department spokesman P.J. Crowley told reporters. "Our actual intent is ... to find ways to pressure the government while protecting the people."
The Prime Minister's Office in Jerusalem has not responded publicly to the State Department's statement. However, senior sources close to Prime Minister Benjamin Netanyahu said that Israel will likely request clarifications in order to ascertain whether the announcement reflects the White House's position.
The US statement appears to constitute a serious blow to Israel's efforts to prompt harsh sanctions against the Islamic republic. In the framework of these efforts, Defense Minister Ehud Barak headed to the US for a series of meetings and talks.
On Wednesday, Barak met with United Nations Secretary-General Ban Ki-moon in the UN's headquarters in New York.
Barak told the secretary-general that "nuclear weapons in Iran will shift the entire strategic balance in the region. We must place debilitating sanctions on Iran, with a restricted time-limit."
Ban expressed support for Israel's desire to prevent the Islamic republic from acquiring nuclear weapons, and promised that the UN will do everything in its power to promote sanctions.
Roni Sofer and Reuters contributed to the report