By Yeganeh Torbati

WASHINGTON (Reuters) - The chief U.S. agency in charge of implementing sanctions has added staff to help speed up processing applications from businesses hoping to trade with Iran, a U.S. Treasury official said on Thursday.

The beefing up of the U.S. Treasury's Office of Foreign Assets Control comes as businesses and lawyers say that often the answers they receive from the agency on whether certain trade is allowed in Iran is vague, non-committal and too slow to facilitate fast-moving business decisions.

Iranian officials have also complained that the country is not bearing the full economic fruits of the deal, and have urged the United States to do more to clarify the sanctions relief and to encourage commercial business deals.

The United States removed many sanctions on Iran in January as part of a landmark deal that also saw Iran curb its nuclear program. But some U.S. sanctions on Iran remain, including a prohibition on U.S. citizens and businesses dealing with the country.

OFAC's acting director, John Smith, said that since the nuclear deal, the agency has received "hundreds if not into the thousands by this point" of applications from businesses seeking licenses to do trade in Iran. Each of those licenses must be assessed by OFAC staff in accordance with complex and overlapping regulations.

"We are stretched to the limit," Smith said, speaking at a forum in Washington, D.C. "We have beefed up our licensing division in substantial ways. We've added more licensing officers. We've just created a new licensing chief to help get licenses out faster."

He did not specify how many new staff, and over what time period, the agency has added.

OFAC staffing levels have stayed relatively consistent at about 170 to 200 people for the last five years or so, former officials say. In the same period, the United States has added dozens of new sanctions programs targeting challenges as varied as cyber attacks, Iran's procurement of ballistic missiles and Russian actions in Ukraine.

"We're doing what we can within the confines of a small government agency that is restricted in our resources," Smith said.

Many applications have to be sent to other U.S. agencies, including the State Department and Commerce Department, for guidance, Smith said, which leads to delayed decisions.

"There are some that are months and they're still waiting,” Smith said. "Those are the tougher calls, often that involve broader foreign policy issues or that involve complex legal issues."

(Reporting by Yeganeh Torbati; Editing by Alan Crosby)