The U.S. State Department is confident that a former FBI agent who went missing in Iran over a month ago is still in that country and has enlisted the aid of other countries to help locate him, a spokesman confirmed Wednesday. "We have assured ourselves to a reasonable degree" that Robert Levinson, who had been regarded as one of the FBI’s most thorough and aggressive agents, is still in the Islamic republic, said State Department spokesman Sean McCormack. "We know that he went there. We’re pretty sure that he didn’t leave," McCormack told reporters. McCormack also said the United States has asked two unnamed European countries, who have diplomatic relations with Tehran, to use their resources and contacts within Iran to try and find Levinson, who disappeared in early March during a visit to the Iranian island of Kish. He said that depending on what information those countries are able to come up with, the U.S. may employ the help of other countries. Click Here for Full Blotter Coverage. The State Department also said that yesterday it received a response from Iran to a U.S. inquiry for any information as to Levinson’s whereabouts. According to McCormack, the one paragraph letter said Iran has no information about Levinson. A senior State Department official, speaking on the condition of anonymity, said the U.S. was skeptical that Iran had no information as to Levinson’s whereabouts, pointing out that the U.S. was able to determine, through its own unspecified means, how Levinson entered Iran and checked into his hotel. The official said that Levinson’s flight information was passed along to Iran in the initial letter. McCormack said that Iran’s response in this case was "unique in recent memory," in that they are unable to provide information about Levinson. He said that two to three Americans go missing per year while traveling in Iran, and in every other case either they have been able to obtain information about them or the person has turned up on their own. McCormack added that the U.S. itself plans to follow up with the Iranians. "We’re doing everything we can as a government to work on behalf of Mr. Levinson," he said. Since the United States does not have diplomatic relations with Iran, that message was delivered through the Swiss government. News reports have said Levinson was in Iran to meet with an American fugitive there on behalf of U.S. documentary producer Ira Silverman. The fugitive, David Belfield, told the Financial Times newspaper that he believed Iranian authorities were holding Levinson and that he was being "well taken care of." McCormack reiterated today that the United States has no information indicating Levinson is being held by the Iranians.