US fighter aircraft F-16 performs aerobatic maneuvers on the last day of Aero India 2019 at Yelahanka in Bangalore, India, February 19, 2019. (AP)

A Pentagon source told Sputnik on Thursday that there are still no updates on whether European allies have established a plan of action to train Ukrainian pilots to use F-16 fighter planes.

"The US will support a joint effort to train Ukrainian pilots on fourth-generation fighter aircraft, including F-16s, as part of our long-term commitment to Ukraine’s self-defense. We have no new announcements to make regarding this effort today," the spokesperson said.

On July 16, the US said it granted permission to its European partners to commence training Ukrainian pilots on fly F-16 fighter jets.

White House National Security Advisor Jake Sullivan confirmed the decision on Sunday and emphasized the US commitment to providing the necessary tools for the training program.

"The president has given the green light, and we will allow, permit, support, facilitate, and, in fact, provide the necessary tools for Ukrainians to begin being trained on F-16s as soon as Europeans are prepared," Jake Sullivan told CNN.

European officials then said that the training program is expected to begin in August in Denmark, and a training facility is set to be established in Romania.

On July 23, US Secretary of State Antony Blinken indicated that Washington is estimating that the Ukrainian counteroffensive will not reach its final stage in the coming weeks and may take several months more, admitting that the counteroffensive has been going "tough".

"These are still relatively early days of the counteroffensive. It is tough… It will not play out over the next week or two. We're still looking, I think, at several months," Blinken told CNN.

US sources reported on Tuesday that the US is still waiting for its European allies to finalize their plan to instruct Ukrainian pilots on F-16 fighter jets. Washington will first have to greenlight the plan before the program can be launched.

On Monday, Ukrainian Defense Minister Oleksii Reznikov said Ukrainian pilots would start their training on F-16 fighter jets this month.

Russian Foreign Minister Sergey Lavrov said in July that Russia will consider the presence of F-16 fighter jets in Ukraine sent from the West as a "nuclear" threat due to their capacity to carry atomic weapons, therefore representing a direct threat to Russia.

"Russia cannot ignore the ability of these aircraft to carry nuclear weapons. No amount of assurances will help here," Lavrov was quoted as saying by the Russian Foreign Ministry.

"In the course of combat operations, our servicemen are not going to sort out whether each particular aircraft of this type is equipped to deliver nuclear weapons or not."

"We will regard the very fact that the Ukrainian armed forces have such systems as a threat from the West in the nuclear sphere."