An Iranian deputy foreign minister echoed the tough talk, saying the Islamic republic, which is accused by the West of trying to build nuclear weapons, was ready for any possible scenario "even for war."
The United States insists it wants a diplomatic solution to the row but has not ruled out military action if that fails. Vice President Dick Cheney said on Saturday Washington and its allies must curb Iran's atomic ambitions.
"Iran has obtained the technology to produce nuclear fuel and Iran's move is like a train ... which has no brake and no reverse gear," Ahmadinejad was quoted by Iran's student news agency ISNA as saying.
Officials from the Security Council plus Germany are due to meet in London in the coming days to examine the chances of drafting a resolution that could impose more restrictions on Tehran. UN sanctions were slapped on Iran in December.
"We have prepared ourselves for any situation, even for war," Manouchehr Mohammadi, one of the deputies to the foreign minister, was quoted by ISNA as saying at a conference in the central city of Isfahan.
"If they issue a second resolution, Iran will not respond and will continue its nuclear activities," he said.
Report: US developing plan to bomb Iran
Despite the Bush administration's insistence it has no plans to go to war with Iran, a Pentagon panel has been created to plan a bombing attack that could be implemented within 24 hours of getting the go-ahead from President George W. Bush, The New Yorker magazine reported in its latest issue.
The special planning group was established within the office of the Joint Chiefs of Staff in recent months, according to an unidentified former US intelligence official cited in the article by investigative reporter Seymour Hersh in the March 4 issue.
The panel initially focused on destroying Iran's nuclear facilities and on regime change but has more recently been directed to identify targets in Iran that may be involved in supplying or aiding militants in Iraq, according to an Air Force adviser and a Pentagon consultant, who were not identified.
The consultant and a former senior intelligence official both said that US military and special-operations teams had crossed the border from Iraq into Iran in pursuit of Iranian operatives, according to the article.
In response to the report, Pentagon spokesman Bryan Whitman said: "The United States is not planning to go to war with Iran. To suggest anything to the contrary is simply wrong, misleading and mischievous.
"The United States has been very clear with respect to its concerns regarding specific Iranian government activities. The president has repeatedly stated publicly that this country is going to work with allies in the region to address those concerns through diplomatic efforts," Whitman said.