Russia said it had arrested 11 people including four suspected gunmen in connection with a shooting rampage that killed 143 people in a concert hall near Moscow, the deadliest attack in Russia for 20 years.

Russian security agency said the attackers had contacts in Ukraine and were driving to the border. “After committing the terrorist attack, the criminals intended to cross the Russian-Ukrainian border, and had appropriate contacts on the Ukrainian side,” the FSB said.

Ukraine’s presidency said Kyiv had “nothing to do” with the attack, while its military intelligence called the incident a Russian “provocation” and charged that Moscow special services were behind it.