A Palestinian medical team took samples from Mr. Arafat’s corpse in the West Bank last year and gave them to Swiss, French and Russian forensic teams in an attempt to determine whether he was killed with the radioactive poison. “He could not have been poisoned with polonium,” the Russian news agency Interfax quoted Vladimir Uiba, who heads the Federal Medico-Biological Agency, as saying. “The research conducted by Russian experts found no traces of this substance.”

However, the agency later denied that it had made an official statement about the research, saying only that it had handed its results to the Russian Foreign Ministry. The Foreign Ministry declined to make any immediate comment. Mr. Arafat died at age 75 of an unexplained ailment he developed while confined to his Ramallah headquarters by Israeli tanks at the height of an armed Palestinian uprising in 2004.