More sanctions on Moscow, more weapons for Ukraine, and a probe into alleged war crimes by Russian soldiers: the United States is upping pressure on multiple fronts against President Vladimir Putin, officials said Monday.As Russia pulls away from the Ukrainian capital Kyiv, leaving behind what Ukraine and its allies authorities say is evidence of mass atrocities, the war is shifting to a focus on eastern regions where Moscow already controls territory and is looking to expand."Russia is repositioning its forces to concentrate its offensive operations in eastern and parts of southern Ukraine," National Security Advisor Jake Sullivan told reporters.

"Russia has tried to subjugate the whole of Ukraine and it has failed.

Now it will attempt to bring parts of the country under its rule."And "this next phase could be measured in months or longer," he said.But while Russian forces have retreated from swaths of northern Ukraine, apparently giving up initial hopes of quickly toppling President Volodymyr Zelensky, the discovery of large numbers of bodies in territory they previously controled is fueling determination in Washington to press even harder.President Joe Biden called Putin a "war criminal" and the killings that occurred in the town of Bucha a "war crime."There should be "a war crimes trial," Biden told reporters.Sullivan said that Washington, in concert with European allies, is also working on more measures to add to the already withering raft of economic sanctions aimed at crippling the ruble, Russia's elite and the country's ability to import high-tech components."You can expect further sanctions announcements this week," he said, adding that "options that relate" to Russia's lucrative energy industry are on the table.Secretary of State of Antony Blinken is traveling to Brussels on Wednesday and Thursday to attend a NATO foreign ministers' meeting.'Advanced weapons'On the ground, the United States is working to increase the volume and apparently the power of weaponry provided to Ukraine's armed forces.For weeks, Zelensky has pleaded for arms able to hit Russian forces from a distance and to defend against Moscow's far stronger air force, navy and long-range artillery.

He has repeatedly stressed a need in particular for fighter jets, tanks and anti-air defenses.While Western powers have so far failed to agree on how or whether to get such systems into Ukraine, partly for fear of provoking Russia, Sullivan noted that the Biden administration has already sent $2.3 billion worth of arms to Ukraine.And he made clear more is on its way.Sullivan said that Washington is working with allies on sourcing weapons including "longer-range anti-aircraft systems, artillery systems and coastal defense systems" — apparently referring to the idea of using Soviet-designed gear held by eastern European countries that could easily be integrated into Ukraine's ranks.He was coy about the details of new systems, which would come on top of the enormous quantities of relatively short-range rockets, drones and small arms already delivered.Sullivan said "some of these systems we cannot advertise."However, "the extent and depth of efforts to acquire and transfer a variety of advanced weapons capabilities is extraordinary, it is unprecedented," he said.