WASHINGTON, (Reuters) – The United States has begun new measures to curb Russia’s evasion of sanctions, said President Joe Biden’s national security advisor on Thursday.

Jake Sullivan, national security advisor to the United States said that evasion is the main focus of his team over the next few days in an interview with the Economic Club of Washington.

Sullivan spoke without providing details, saying that he believed there would be some announcements over the coming weeks to identify potential targets for facilitating evasion inside Russia as well as outside Russia.

He stated that Russia could try to block weapons transfers for Ukraine, which would only escalate tensions with the West.

“The United States doesn’t operate within the Ukraine territory. So if the Russians were to strike NATO territory (where materiel is being assembled), that would invoke Article 5 and be a game changer.”

According to Article 5, an attack against one NATO member is considered an attack upon all its members. This clause was invoked once after the attacks of September 11, 2001 on the United States.

Sullivan claimed that a Russian-claimed missile cruiser had been attacked on Thursday by Ukraine, which was a major blow for Russia.

He said, “We have been in contact with the Ukrainians over the night. They had stated that they hit the ship with antiship missiles.” Although we don’t yet have the ability to confirm this independently, Russia is clearly hurt by the events.

Russia’s defense ministry claimed that the Moskva was the vessel carrying the most important part of its Black Sea fleet. However, it did not say that an attack had occurred. Reuters couldn’t verify statements from either side.

Sullivan refused to comment on whether or not a senior U.S. official will soon visit Kyiv as other leaders, including the British Prime Minster Boris Johnson, have done recently. He stated that the conflict in Ukraine might continue for many months or even longer.