Ukraine’s counteroffensive, which is still in its early stages, is not meeting the expectations of Kyiv’s allies, Western officials told CNN News on Thursday. 

According to Western assessments, Russia has fortified its lines of defense much better than expected. Moscow is also using air attacks and mines to complicate the advancement of the Ukrainian army.   

So far, the counteroffensive is “not meeting expectations on any front,” one of the sources told CNN. Ukrainian forces are proving “vulnerable” to minefields and Russian forces “competent” in their defense, one of the Western officials added.

Nevertheless, Washington and its allies “remain optimistic” that Ukraine will be able to recapture occupied territory with time, according to the report. Kyiv’s allies are likely to wait until at least July for a fuller assessment of the progress of the counteroffensive.

The officials also noted that Ukrainian forces have been adapting to Russian tactics and defenses, including carrying out more dismounted operations. In recent days, Ukrainian forces have also had more success targeting and shooting down Russian aircraft.

Overall, the counteroffensive is a “tough drive” for both warring sides, who suffer heavy losses, one of the Western officials said. Earlier on Thursday, Russia’s FSB security service head Nikolai Patrushev told Russian President Vladimir Putin that Ukraine has lost 13,000 servicemen since the beginning of its counteroffensive. 

Ukrainian President Volodymyr Zelensky on Wednesday also said that progress had been “slower than desired.”

“We would definitely like to make bigger steps,” Zelensky told BBC, adding, however, that “those who fight shall win and to those that knock, the door shall be opened.”