Russian President Vladimir Putin has claimed, once again, that Ukrainians are committing sabotage inside his country. He is promising a crackdown in response to what he calls a "terrorist" attack.

Russian authorities say an armed group of "Ukrainian nationalists" crossed the border and opened fire in the western region of Bryansk on Thursday. They say two civilians were killed. They describe the killings as "murder" and say the attackers used "NATO weapons."

On Friday, Putin called on members of his Security Council to come up with tougher measures.

Putin said, "Today, we have one very important question -- for the anti-terrorist protection of facilities under the jurisdiction of law enforcement agencies."

Border guards in the Bryansk region have increased security.

However, Ukrainian officials deny responsibility for the attack. They say it could have been an operation staged by Russian partisans as a "provocation."