U.S. officials have also been deeply concerned about Iran's nuclear weapons program, which has the support of both elected reformers and conservative clerics. The [Bush] administration has pressed the International Atomic Energy Agency, the U.N. nuclear watchdog, to issue a critical report next month on Iran's nuclear activities. Officials have sought to convince Russia and China -- two major suppliers of Iran's nuclear power program -- that Iran is determined to possess nuclear weapons, a campaign that one U.S. official said is winning support.

Earlier this week, Defense Secretary Donald H. Rumsfeld accused Iran of harboring al Qaeda members. "There's no question but that there have been and are today senior al Qaeda leaders in Iran, and they are busy," Rumsfeld said. Iranian officials, however, have vehemently denied that they have granted al Qaeda leaders safe haven in the country.

Until the Saudi bombings, some officials said, Iran had been relatively cooperative on al Qaeda. Since the Sept. 11, 2001, attacks, Iran has turned over al Qaeda officials to Saudi Arabia and Afghanistan. In talks, U.S. officials had repeatedly warned Iranian officials that if any al Qaeda operatives in Iran are implicated in attacks against Americans, it would have serious consequences for relations between the two countries.