Kyiv, Ukraine - Russian President Vladimir Putin warned the West on Thursday that letting Ukraine use longer-range weapons to strike targets inside his country would put NATO "at war" with Russia.

The stark warning came as US and UK officials discussed Kyiv's demand for them to ease rules on firing Western weapons into Russia more than two and a half years into Moscow's invasion of Ukraine.

Moscow meanwhile also claimed to have recaptured a swath of territory in its western Kursk region, where Ukrainian forces had made advances in recent weeks.

Putin spoke after US Secretary of State Antony Blinken promised that Washington would quickly review Kyiv's long-standing request for more leeway to use Western-supplied weapons to strike Russian targets.

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"This would in a significant way change the very nature of the conflict," Putin told a state television reporter.

"It would mean that NATO countries, the United States, European countries, are at war with Russia," he said.

"If that's the case, then taking into account the change of nature of the conflict, we will take the appropriate decisions based on the threats that we will face."

Speaking at a press conference in Warsaw on Thursday, Blinken said the US would "adjust, we'll adapt as necessary, including with regard to the means that are at Ukraine's disposal to effectively defend against the Russian aggression."