US Secretary of State Antony Blinken indicated on Sunday 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.

Ukraine launched its much-touted counteroffensive in early June after repeatedly delaying the campaign over a lack of military supplies from its Western donors. Zelensky had admitted that progress was "slower than desired."

In mid-July, Blinken said Ukraine’s counteroffensive is in its "early weeks" and will "play out over the next weeks."

The Russian Defense Ministry said Ukrainian troops have been trying — but failing — to advance in the South Donetsk, Bakhmut, and Zaporozhye directions.

Earlier on Sunday, Russian President Vladimir Putin reiterated, during talks with his Belarusian counterpart Alexander Lukashenko in St. Petersburg, that the Ukrainian counteroffensive has failed.

Touching on the delivery of US F-16 fighter jets to Kiev, Blinken reiterated that the US will deliver the warplanes to Ukraine but the process will take "several months" as it involves providing training and maintenance.

"If a decision were made to actually move forward on the F-16s tomorrow, it would be months and months before they were actually operational," the top US diplomat said.

On Thursday, White House National Security Council spokesperson, John Kirby, said Ukraine would receive F-16 by the end of the year.

Earlier in July, Pentagon’s Joint Staff Director for Operations Lt. Gen. Douglas Sims pointed out that the conditions on the battlefield in Ukraine were not "ideal" for using F-16 fighter jets, given that Russia continues to possess air defense capabilities.

Read more: West knew Kiev lacked preparedness for counteroffensive: WSJ

US not viewing sanctions on Chinese Defense Minister as obstacle for talks

In a separate context, Blinken said the United States does not view sanctions against the Chinese military leadership as a stumbling block in maintaining contacts between the two countries' defense departments, calling Beijing's unwillingness to engage in such contacts "a political decision."

"Those sanctions don't prevent the [Chinese Defense] minister [Li Shangfu] from engaging or us engaging with him… it is a political decision, in effect, for China to decide whether or not he should be engaging," Blinken told CNN.

He went on to say that Washington "made very clear" to Beijing that maintaining bilateral military-to-military contacts was "a responsibility" to avoid any miscalculations and wrong perceptions.

In June, a spokesperson for the Chinese Embassy in Washington made it clear that the United States should lift its unilateral sanctions on China to revive military-to-military contacts, stressing that Beijing never rejected communication with Washington.