Iranian President Mahmoud Ahmadinejad would not be welcome at the upcoming Nuclear Non- Proliferation Treaty (NPT) Review Conference if he tries to use the conference as a platform for lobbying against UN sanctions, U. S. Secretary of State Hillary Rodham Clinton warned on Thursday.

"The mission of those of us going to New York to review, revise and reinvigorate the NPT regime is very clear. If that's not his mission, then it won't be a particularly useful or productive trip on his part," Clinton told reporters at the State Department.

"If he believes that by coming he can somehow divert attention from this very important global effort or cause confusion that might possibly throw into doubt what Iran has been up to ... then I don't believe he will have a particularly receptive audience," she said.

At the NPT review conference, the Obama administration is expected to try making all the participants reaffirm their commitment to the NPT treaty and to strengthen its three pillars: non-proliferation, disarmament, and peaceful uses of nuclear energy.

U.S. State Department said Wednesday that it would not block President Ahmadinejad's application for a visa to attend the NPT conference, which begins next Monday at the UN Headquarters in New York.

As to Iran's nuclear program, the United States, Israel and other Western countries worry that Tehran may obtain the uranium fuel needed for nuclear weapons by the same process to purify uranium. But Iran insists its nuclear program is for peaceful purpose.

The Obama administration has been trying to push the fourth round of sanctions on Iran under the framework of the United Nations in the coming days, in an attempt to make Iranian leaders realize the "importance of changing their actions and decisions concerning their nuclear program."