Ukraine has U.S. weapons it can't use in Russian territory. Will that change?

Ukraine is trying to fend off a Russian offensive in the northeastern border region of Kharkiv, but it can only use its U.S.-provided firepower on its own side of the border when trying to thwart attacks.

That's because Washington has put guardrails around where its weapons are to be used, and that is in Ukraine only — though the pressure is building for the U.S. to give Kyiv a freer hand to operate.

Ukrainian politicians travelled to the U.S. capital this week to press the Biden administration to change its thinking on the issue. And the U.S. Helsinki Commission, a federal agency that promotes human rights and military security, said the U.S. should "not only allow, but encourage" Ukraine to use these weapons across the Russian border.

But analysts don't necessarily see Kyiv as being likely to get the sign-off it's seeking, given Washington's worries over escalation risks and the so-called red lines around the conflict — that NATO will stay out of Russia, but also will defend "every inch" of its members' territory. Though Ukraine is not part of NATO, it lies on the edge of several members of the military alliance.

"These constraints were established right at the beginning," said Janice Stein, a foreign policy expert and the Belzberg professor of conflict management at the University of Toronto. "And so far, they are being respected."

Together, those conditions leave Ukraine trying to manage the threats against it without crossing those same red lines.

"This whole conflict has been driven by the U.S. policy to try to help Ukraine defend, without getting into a confrontation with Russia by helping Ukraine attack," Wesley Clark, a retired U.S. general and former supreme commander of NATO, told CNN. "And so, Ukraine is being forced back. Its forces are being bled out."

Kyiv rushed reinforcements to the Kharkiv region amid a wave of Russian attacks — including airstrikes, shelling and troops on the ground — that have forced thousands of Ukrainians living near the border to flee. 

The fighting has been fierce, with Ukrainian President Volodymyr Zelenskyy telling ABC News that hundreds of Ukrainian soldiers have been wounded in recent days.

"A lot of guys gave their lives," Zelenskyy told the network Thursday, the day he met with military leaders in Kharkiv and visited injured soldiers.

Ukrainian officials say the armed forces have stopped Russian advancements in Kharkiv, and NATO's top commander, Gen. Christopher Cavoli, has said Russia does not have sufficient forces in place to make "a strategic breakthrough" there.

Yet Russian President Vladimir Putin claimed Friday that his forces are aiming to create a buffer zone against Ukrainian attacks on the Russian Belgorod region, which he said were the reason for the Kharkiv offensive.

And he said Moscow has no plans to capture the city of Kharkiv itself, the regional capital.

The U of T's Stein said Ukraine is dealing with the urgent problems in Kharkiv despite dwindling air-defence supplies and ammunition, which Western allies are working to replenish — but which should have happened sooner.