In this image provided by the US Army, soldiers conduct live fire testing at White Sands Missile Range, N.M., on Dec. 14, 2021, of early versions of the Army Tactical Missile System. (AP)

European Union foreign policy chief Josep Borrell confirmed on Monday that Kiev had received approval from the United States to launch strikes up to 300 kilometers (186 miles) into Russian territory.

"The [US President Joe] Biden administration has authorized the use of its weapons up to 300 kilometers into Russian territory, so up to 300 kilometers radius," Borrell said following a meeting of EU foreign ministers in Brussels.

EU foreign ministers have deliberated on the US authorization for Kiev to conduct strikes deep into Russian territory, but no consensus has been reached on the matter, Borrell added.

On Sunday, The New York Times reported, citing unnamed US officials, that President Joe Biden had granted Ukraine permission to use American long-range missiles to target deep Russian soil for the first time. According to the sources, the initial strikes deep into Russia are expected to be carried out using ATACMS missiles.

The United States anticipates that Ukraine will focus its use of long-range ATACMS missiles "primarily" on Russia's Kursk region, CNN reported on Monday, citing a US official.

The Biden administration has disclosed little information regarding its decision to approve Ukraine's use of US-supplied long-range missiles against Russian territory, the report added.

According to the Institute for the Study of War, about 250 Russian military targets, including 17 airbases, fall within the range of Ukrainian ATACMS missiles, the report stated.

Biden sparks backlash

Meanwhile, backers of US President-elect Donald Trump took to social media on Sunday to voice their reactions to the reports, accusing Biden of escalating the conflict further during his last months in office.

"As President Trump has said on the campaign trail, he is the only person who can bring both sides together in order to negotiate peace, and work towards ending the war and stopping the killing," Trump Communications Director Steven Cheung told Newsweek.

Kremlin spokesperson Dmitry Peskov stated that if the authorization to strike deep into Russia is confirmed and relayed to Ukraine, it would signal a new escalation in tensions. He also reiterated that Russian President Vladimir Putin had clearly outlined Moscow's position on the use of long-range weapons targeting Russian territory.

Putin had warned that such a decision would be regarded as direct involvement by the United States and other NATO countries, fundamentally altering "the very nature of the conflict."