ROME, Dec. 24 (AP) — An Italian who met with a Russian former K.G.B. operative the day the man fell ill from radiation poisoning was arrested on Sunday, the Italian’s father said.

The accusations of international arms trafficking and slander against the Italian, Mario Scaramella, were not believed to be directly related to the investigation into the poisoning death of the former Russian agent, Alexander V. Litvinenko.

Mr. Scaramella, who is the first person connected to the poisoning case to be arrested, met Mr. Litvinenko at a London sushi bar on Nov. 1, the day the Russian fell ill. Mr. Litvinenko died of poisoning from radioactive polonium 210 on Nov. 23.

The Italian’s father, Amedeo Scaramella, said his son was arrested in Naples after returning from London. Rome prosecutors have accused him of international arms trafficking and slander, and he is being taken to Rome, his father said.

Mario Scaramella’s lawyer, Sergio Rastrelli, told the RAI Tg1 television news that his client was scheduled to be questioned Wednesday. Mr. Rastrelli said he expected that Mr. Scaramella would tell investigators that all of his actions were “legitimate and rightful.”

Mr. Scaramella has said that at the Nov. 1 meeting, he showed Mr. Litvinenko e-mail messages from a confidential source identifying the possible killers of a Russian investigative journalist, Anna Politkovskaya, and listing other potential targets for assassination, including himself and Mr. Litvinenko.

On his deathbed, Mr. Litvinenko blamed President Vladimir V. Putin of Russia for his poisoning, an accusation that the Kremlin denied.

Mr. Scaramella also was hospitalized in London, and he said doctors told him that he had received five times the lethal dose of polonium 210, although he showed no symptoms. He left the hospital a few days later.