This was announced by White House National Security Adviser Jake Sullivan and Pentagon spokesman Maj. Gen. Patrick Ryder.
Sullivan said the authorization extends to "any place where Russian troops cross the border" to take control of new Ukrainian territory.
"This is not about geography. It's about common sense. If Russia is attacking or is going to attack Ukraine from its territory, it makes sense to allow Ukraine to retaliate against forces that are attacking it from across the border," he said.
The U.S.-Ukraine agreement now applies "wherever Russian forces cross the border from the Russian side into the Ukrainian side to seize additional Ukrainian territory," national security adviser Jake Sullivan told PBS.
At the same time, a source told Politico that Washington's ban on striking deep into Russia with long-range weapons remains in place.
On May 10, Russian units entered Kharkiv Oblast. Although their advance was quickly halted, including by U.S. ammunition and equipment from a new aid package that began arriving at the front, the Ukrainian military also says it threatens to invade the western Sumy region.
If that happens, U.S. authorization would extend to strikes on Russian territories bordering it, Sullivan said. These include not only Belgorod, but also Kursk and Bryansk regions.
