-based think tank Institute for the Study of War (ISW) assessed on April 21.Although the ISW expects Russia's intensified attacks will continue in the coming weeks ahead of the anticipated arrival of resumed U.S. military aid, the ISW notes that the anticipated military aid for Ukraine must be delivered quickly to quell the expected offensive. "Russian forces will likely intensify ongoing offensive operations and missile and drone strikes in the coming weeks in order to exploit the closing window of Ukrainian materiel constraints," the report assesses, adding that Ukraine "will likely be able to blunt the current Russian offensive assuming the resumed U.S. assistance arrives promptly."The ISW's assessment comes as U.S. Senator Mark Warner told CBS News on April 21 that the United States could begin transferring long-range Army Tactical Missile Systems (ATACMS) to Ukraine "by the end of the week.