As Ahmadinejad visited New York for the UN General Assembly, the United States has sharpened the tone against his regime with senior officials publicly saying that economic sanctions have weakened the firebrand leader.

Opening his trip, Ahmadinejad called in an interview on September 19 for the US to release eight Iranians as a "humanitarian gesture" after the Islamic republic freed US hiker Sarah Shourd.

State Department spokesman Mark Toner rejected any link.

"We would just say that there is no equivalent between these individuals who have been either charged or tried and afforded due process in a court and these hikers who crossed an unmarked border and have yet to be charged," Toner told reporters.

Shourd, 32, returned to the United States after more than a year in detention, but two fellow hikers remain in custody. The hikers say they strayed into Iran in July 2009 from Iraqi Kurdistan. But Iranian authorities have alleged that they were spying.

AFP