Russian President Vladimir Putin marks the Defender of the Fatheland Day in 2015 in central Moscow, Russia, with military officials surrounding him.Sasha Mordovets | Getty Images News | Getty ImagesWASHINGTON – The Biden administration warned Monday that Russian forces are expected to intensify their military operations in Ukraine after weeks of stalled ground advances.”When Russia started this war, its initial aims were to seize the capital of Kyiv replace the Zelenskyy government and take control of much if not all of Ukraine,” national security advisor Jake Sullivan told reporters at the White House, adding “Russia believed that it could accomplish these objectives swiftly and efficiently.”He said U.S. officials believe Russia’s revising its goal in the war. “Russia is repositioning its forces to concentrate its offensive operations in eastern and parts of southern Ukraine, rather than target most of the territory,” Sullivan said, citing failed Russian attempts to capture Kyiv.For the past five weeks, Russian forces on the ground in Ukraine have been beset with a slew of logistical problems on the battlefield, including reports of fuel and food shortages.”All indications are that Russia will seek to surround and overwhelm Ukrainian forces in eastern Ukraine. We anticipate that Russian commanders are now executing the redeployment from northern Ukraine to the region around the Donbas,” Sullivan added.He added that Russia’s renewed ground offensive in eastern Ukraine will likely also “include air and missile strikes across the rest of the country to cause military and economic damage, and frankly, to cause terror.”FILE PHOTO: An aerial view shows a residential building destroyed by shelling, as Russia’s invasion of Ukraine continues, in the settlement of Borodyanka in the Kyiv region, Ukraine March 3, 2022. Picture taken with a drone. Maksim Levin | ReutersA senior U.S. Defense official, who spoke on the condition of anonymity to share details of the Pentagon’s thinking, said that the Kremlin moved about 65% of its forces near Kyiv to Belarus.The official said the Pentagon believes those Russian troops are being resupplied with additional manpower in Belarus before deploying back to the fight in Ukraine. When asked where the troops would likely go, the official said that the Pentagon believes the majority of them will move to the Donbas region.The Defense official added that the U.S. believes the “vast majority” of Russian forces are still in Ukraine and that Kyiv is still under threat.Later on Monday, Pentagon spokesman John Kirby declined to say how exactly Russian forces are going to reorganize before deploying back into parts of Ukraine.”We don’t believe that this is a complete withdrawal from the war effort. These guys are not going home, I guess is the main point,” Kirby said, adding that the Pentagon was “not able to perfectly predict exactly how they’re going to reform their units” though.When pressed, Sullivan declined to provide a timeline of how long Russia’s war in Ukraine would last.”It may not be just a matter of a few more weeks,” Sullivan said. “This next phase could be measured in months or longer,” he added.