The United States has dismissed a suggestion by President Mahmoud Ahmadinejad to free Iranians in exchange for two detained hikers as Washington kept up pressure on the Islamic republic. 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 Sunday for the United States to release eight Iranians as a humanitarian gesture after the Islamic republic freed US hiker Sarah Shourd. Meanwhile, the State Department spokesman Mark Toner rejected any link.