Britain, France and Germany said Wednesday Iran faces further sanctions if it refuses to cooperate with the U.N. nuclear agency, which cites “credible” evidence of Iranian efforts to design a nuclear weapon.

A report released Tuesday by the International Atomic Energy Agency expresses “serious concern” about information indicating that Iran has worked on a nuclear weapon design, including the “testing of components.”

Iranian President Mahmoud Ahmadinejad told a nationally-televised rally on Wednesday that his country will not retreat “one iota” from its nuclear path.

The report contains the U.N. agency's strongest and most detailed allegations yet of military dimensions to Iran's nuclear program. In his remarks Wednesday, Mr. Ahmadinejad rejected the report, saying it contains “absurd” U.S. claims.

The United Nations has imposed four rounds of sanctions on Iran for refusing to stop nuclear activities that could have civilian and military uses. Western powers say they want to prevent Iran from becoming nuclear-armed, but Tehran insists its nuclear program is peaceful.

Russia, however, said Wednesday it will not support new sanctions.

But British Foreign Secretary William Hague said Wednesday London is considering “additional measures” to increase pressure on Iran if it does not “change direction.” French Foreign Minister Alain Juppe also warned of “unprecedented” sanctions if Iran refuses to address international concerns about its nuclear program.

German Foreign Minister Guido Westerwelle said if Iran continues to ignore Western concerns, stronger sanctions will be inevitable.

China said Wednesday it is studying the IAEA report and called for dialogue and cooperation among all the parties in the nuclear dispute.