WASHINGTON - The U.S. government on Friday pressed Iran for help to locate a former agent of the Federal Bureau of Investigation (FBI) who went missing six years ago in the Islamic country.

In a statement on the sixth anniversary of the disappearance of the agent, Robert Levinson, the White House said that finding Levinson "remains a high priority for the United States, and we will continue to do all that we can to bring him home safely to his friends and family."

"The Iranian government previously offered assistance in locating Levinson and we look forward to receiving this assistance, even as we disagree on other key issues," the statement said. In order to find Levinson, who went missing during a business trip to Iran's Kish Island on March 9, 2007, the FBI offered a 1-million-U.S-dollar reward last year for information leading to his safe return. "This year, we again reaffirm our commitment to bringing him home to those who love him," the White House added.

U.S. Secretary of State John Kerry also issued a statement on the disappearance of Levinson, a father to seven children and a grandfather of two.

"The United States continues to welcome the assistance of our international partners in this investigation and calls on the government of the Islamic Republic of Iran to uphold its offer to help find Mr. Levinson and return him safely to his family," Kerry said.

The top U.S. diplomat said that he met with Levinson's wife and son on Friday "to reiterate that the U.S. government remains committed to locating Mr. Levinson and reuniting him safely with his family."

The relations between United States and Iran are strained over Tehran's nuclear programme, which Washington regards as an attempt to make nuclear weapons despite Iran's repeated declarations of the peaceful nature of its nuclear initiative.

The Obama administration, which has imposed crippling economic sanctions against Iran, refuses to exclude the use of force to prevent Tehran from acquiring a nuclear bomb.