Russia on Tuesday deepened its accusations against Ukraine and its Western allies, claiming again, without evidence, that they were most likely involved in the terrorist attack on a concert hall near Moscow that killed at least 139 people.

Aleksandr Bortnikov, the director of the Federal Security Service, the top security agency in Russia, said that the assault “was prepared by both radical Islamists themselves and, naturally, facilitated by Western special services.”

The Islamic State has claimed responsibility for the attack, and eight people have been arrested in connection with the assault.

According to the state news agency Tass, when asked whether Russia believed the United States, Britain and Ukraine were involved in the attack, Mr. Bortnikov said “we believe that’s the case.”

“Overall, we believe that they were involved in this,” Mr. Bortnikov told journalists, referring to Ukraine. He said that his accusations were still based on preliminary information.

The Ukrainian government has denied it was involved in the assault. Speaking about Mr. Bortnikov’s statements, Mykhailo Podolyak, a senior Ukrainian presidential aide, called them “lies.”