The directive marks a policy shift but could potentially escalate tensions with the Kremlin, which has been threatening retaliatory action.

United States President Joe Biden has eased a ban on Ukraine using US weapons inside Russian territory to help the country defend its northeastern Kharkiv region from attack.

Several US officials, speaking on condition of anonymity, told multiple media outlets on Thursday that Kyiv would be allowed to use the weapons on the border of the Kharkiv region which came under renewed Russian attack earlier this month.

The decision marks a policy shift by Biden who had refused to let Kyiv use US weapons beyond Ukraine’s borders, and comes as France and other European countries indicated Ukraine would be allowed to use their weapons on military targets inside Russia.

Amid the debate, Russian President Vladimir Putin on Tuesday warned of “serious consequences”, stressing his country’s nuclear strength, if Ukraine’s Western allies loosened their policy,

There was no immediate comment from Moscow on Biden’s decision, under which Kyiv will be authorised to strike military targets on the border with the Kharkiv region, where Russia has overrun a number of villages since May 10, forcing the evacuation of thousands of residents.

“The president recently directed his team to ensure that Ukraine is able to use US-supplied weapons for counter-fire purposes in the Kharkiv region so Ukraine can hit back against Russian forces that are attacking them or preparing to attack them,” a US official told the Reuters, AFP and The Associated Press news agencies. The change was first reported by online media outlet Politico.

Ukrainian President Volodymyr Zelenskyy has been urging Kyiv’s allies to allow it to use their longer-range weaponry to hit targets on Russian soil amid a surge in attacks this month, particularly on Kharkiv, Ukraine’s second-largest city, some 30 kilometres (19 miles) from the border with Russia.

A Russian attack at midnight (21:00 GMT) killed at least three people and injured 16 after a Russian missile hit an apartment block in the city. Last weekend, 19 were killed after a Russian attack on a hardware superstore.

“The Biden administration has come a long way from their hypersensitivity to and misunderstanding of the risk of escalation,” Alexander Vindman, a retired army lieutenant colonel and former director for European affairs at the White House National Security Council under the Trump administration, told the Reuters news agency.

He applauded the shift in Biden’s policy, which he said “unties Ukraine’s hands”.

“Of course, it’s the right move,” Vindman said.

The US is the biggest supplier of weapons to Ukraine in its battle to push back the Russian military, which began a full-scale invasion of the country in February 2022.

The Biden decision came hours after NATO chief Jens Stoltenberg told the alliance’s foreign ministers that the “time had come” to relax the restrictions placed on Kyiv over the use of the weapons and “enable Ukrainians to really defend themselves”.

“We need to remember what it is,” he said. “This is a war of aggression launched by choice by Moscow against Ukraine.”

The right to self-defence, Stoltenberg added, ” includes also striking legitimate military targets outside Ukraine”.

The officials said Washington would continue to prohibit Ukraine from using ATACMS, which have a range of up to 300km (186 miles), and other long-range US weapons for attacks deep inside Russia.

Moscow has been using missile launchers and other military sites just inside its border with Ukraine to support its offensive in the Kharkiv region, while fighter aircraft have been used to unleash glide bombs on Kharkiv itself, which was home to about 1.5 million people before the war.

On Thursday, Ukraine’s top military commander Oleksandr Syrskii said Russia was moving additional regiments and brigades to the north of the Kharkiv region, just across the border.