The collapse in crude oil prices only adds to the strain on the Iranian economy brought on by Western sanctions, U.S. Vice President Joe Biden said.

Biden addressed delegates at a Middle East forum supported by the Brookings Institution in Washington D.C., saying a joint action plan meant to curb Iran's nuclear ambitions was working.

"The joint plan of action is not a perfect or permanent solution," he said in his Sunday remarks. "But it provides us time to negotiate, to see if it's possible to reach a comprehensive agreement that can peacefully ensure that Iran will not develop a nuclear weapon."

Iran under the terms of the agreement can export about 1 million barrels of oil per day and tap into some oil revenue accounts that were frozen under previous sanctions efforts. Iran in return agrees to curb some of its nuclear research activity.

Biden said if Iran takes the steps necessary to prove its nuclear program is peaceful, it can receive more relief from sanctions pressure.

"In the meantime, make no mistake about it: the Iranian economy remains under tremendous pressure [because of sanctions]," he said.

The World Bank said in an October report the Iranian economy is contracting, but at a slower pace than before. Sanctions imposed on the Iranian energy sector in response to its nuclear program resulted in a real gross domestic product contraction of 5.8 percent last year.

Biden added that Iran is out more than $35 billion in oil revenue since it agreed to the joint action plan in November 25. Since June 2012, the value of the Iranian currency has dropped about 50 percent.

Last week, Iranian officials said they were drafting a budget for the fiscal year that begins in March based on $70 per barrel. Oil prices in June were hovering around the $110 per barrel mark.

"The bottom falling out of oil prices has further complicated Iran's economic outlook," Biden said.