President Zelenskyy says Ukrainian counteroffensive is 'advancing' but 'we want to do it faster'

KYIV, Ukraine -- Ukraine's ongoing counteroffensive has allowed their forces to take the "initiative" in the war against Russian invaders but "we want to do it faster," President Volodymyr Zelenskyy told ABC News' Martha Raddatz in a wide-ranging new interview previewed on "Good Morning America" on Thursday.

"What is your assessment of how the counteroffensive is going right now?" Raddatz, ABC News' chief global affairs correspondent, asked Zelenskyy in the sit-down from his nation's capital.

He said that he supported his military's assessment that the operation, which began in earnest last month, was "going to plan."

"We would all like to see the counteroffensive accomplished in a shorter period of time, but there's reality," he said. "We are advancing. We are not stuck in one place."

While Ukraine has succeeded in liberating a number of villages in recent weeks, progress has not matched the lightning speeds of last fall's campaign -- which saw Ukraine reclaim thousands of square miles of territory in one week in the Kharkiv region, Ukrainian officials said at the time.

"Today, the initiative is on our side," Zelenskyy told Raddatz. "We are advancing, albeit not as fast [as we would like]. But we are advancing."

Raddatz also asked about whether Ukraine can succeed without F-16s, the fighter aircraft Ukraine has asked for but not yet been provided and if the U.S. and others had been too slow to provide critical military equipment.

More from Raddatz' interview with Zelenskyy in Ukraine will air on ABC's "World News Tonight with David Muir" on Thursday and on "This Week with George Stephanopoulos" on Sunday.

“F-16 or any other equipment that we do need will give us an opportunity to move faster, to save more lives, to stand our ground for a longer time,” Zelenskyy said. “Well, some weapons have been provided, on the other hand, helps us save lives and we appreciate that. Of course, foot dragging will lead to more lives lost.”

Despite the grinding progress and heavy losses, Ukraine's military leaders remain confident that the operation, seen as key to securing a satisfactory peace, has been proceeding as expected, Zelenskyy said.

The U.S. has been a key ally as Ukraine has prepared to push back into occupied territory. Last week, U.S. Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, warned that the new offensive is "going to be very difficult, it's going to be very long and it's going to be very, very bloody."

Zelenskyy told Raddatz in Kyiv that it was "too early" to report major successes on the battlefield.

Analysts suggest that Ukraine is keeping a large proportion of its assembled forces in reserve -- with the hope of launching a major attack once a weak point has been identified along the front lines, which stretch for thousands of miles through eastern Ukraine.

Gen. Oleksandr Syrskyi, commander of the Ukrainian ground forces, expressed confidence when he was asked by Raddatz earlier this week if he was confident of retaking the key city of Bakhmut. "Yes, of course," he said. "I'm sure."