The FBI said Friday that a Nevada man's claim that his cellular phone picked up people talking in Arabic about a planned terrorist attack was "not credible."

"The results of the investigation to date do not substantiate these allegations and the FBI has determined that this information is not credible," Ellen Knowlton, special agent in charge of the Las Vegas FBI office, said in a statement.

FBI Special Agent Daron Borst called the investigation "substantially complete" after agents spent 4 hours questioning Michael Hamdan and giving him a polygraph test Friday. Borst declined to discuss results of the test or elaborate further about the investigation.

Hamdan, 54, told The Associated Press that he failed the lie-detector test.

"They told me everything was OK, but there was some uncertainty about a few things," Hamdan said as his wife drove him to their home in suburban Henderson following the test.

Hamdan, who was born in Lebanon and speaks Arabic, stuck by his story during the interview with the AP.

He said that on June 15 he overheard Arabic-speaking men say to another, "We are in the city of corruption, the city of prostitution, the city of gambling, the city of unbelievers."

Hamdan said he believed the men were referring to Las Vegas and that one who said, "We are going to hit them on the day of freedom" meant a terrorist attack was planned for July Fourth.