Britain, France and Germany said Wednesday Iran faces further sanctions if it refuses to cooperate with U.N. nuclear experts who say they have “credible” evidence of Iranian efforts to design a nuclear weapon.

The International Atomic Energy Agency released a report Tuesday expressing “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. He also rejected the IAEA report, saying it contains “absurd” U.S. claims. The report represents the U.N. agency's strongest and most detailed allegations yet of military dimensions to Iran's nuclear program.

Israeli Prime Minister Benjamin Netanyahu issued a statement Wednesday urging the international community to stop what he called Iran's pursuit of nuclear weapons, which he says endangers the peace of the world and the Middle East.

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

Russia said Wednesday it will not support a new round of sanctions.

Deputy Russian Foreign Minister Gennady Gatilov told the Interfax news agency that Moscow believes new sanctions will be seen in the international community as a pretext to try to pursue “regime change” in Iran.

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.