The United States and several European countries are pushing for the U.N. nuclear watchdog to come down hard on Iran for its nuclear program.

The International Atomic Energy Agency's 35-nation board of directors opens a two-day meeting in Vienna Thursday, the agency's first gathering since it alleged last week there is “credible” evidence Tehran is trying to build nuclear weapons.

Diplomats negotiated throughout the day Wednesday on a resolution on Iran's nuclear activities. Western diplomats have been pushing for a strongly worded condemnation of Tehran but say they have run into resistance from Russia and China.

Both Moscow and Beijing have expressed skepticism of last week's IAEA report, with Russian officials dismissing the findings as nothing new.

Iran itself rejected the report and has continually denied allegations it is pursuing nuclear weapons.

Recent reports in the Israeli media said Israel's government has been considering a military strike on Iran's nuclear sites. And Israeli Defense Minister Ehud Barak warned during a U.S. television interview that Iran could spark a new, nuclear arms race if it gets a nuclear bomb.

Last week, U.N. Secretary-General Ban Ki-moon called for Iran's nuclear dispute with the West to be resolved through negotiations. Mr. Ban's spokesman said diplomacy is the “only way” to settle the issue.

Iran's Supreme Leader Ayatollah Ali Khamenei has said Tehran will respond to any military strike by Israel or its main ally the United States with “strong slaps and iron fists.”

Britain, France and Germany have warned Iran will face additional sanctions if it refuses to address international concerns about its nuclear work.

The U.N. Security Council has passed four sets of sanctions on Iran for refusing to stop nuclear activities that have both civilian and military uses.