KYIV (Reuters) -Ukraine signalled on Friday that the main push in its counteroffensive against Russian forces was still to come, with some troops not yet deployed and the operation so far intended to "set up the battlefield."

And one of its top generals reported "tangible successes" in advances in the south - one of two main theatres of operations, along with eastern Ukraine.

Ukraine says it has retaken eight villages in the early stages of its most ambitious assault since Russia's full-scale invasion 16 months ago, but President Volodymyr Zelenskiy said this week that gains had been "slower than desired."

Addressing the pace of the Ukrainian advances, three senior officials on Friday sent the clearest signal so far that the main part of the counteroffensive has not yet begun.

"Offensive operations of the Armed Forces of Ukraine continue in a number of areas. Formation operations are underway to set up the battlefield," presidential adviser Mykhailo Podolyak said on Twitter.

"The counteroffensive is not a new season of a Netflix show. There is no need to expect action and buy popcorn."

Deputy Defence Minister Hanna Maliar said the "main events" of the counteroffensive were "ahead of us."

"And the main blow is still to come. Indeed, some of the reserves - these are staged things - will be activated later," Maliar told Ukrainian television.

General Oleksandr Tarnavskyi, commander of Ukraine's "Tavria," or southern front, wrote on Telegram: "There have been tangible successes of the Defence Forces and in advances in the Tavria sector."

Tarnavskyi said Russian forces had lost hundreds of men and 51 military vehicles in the past 24 hours, including three tanks and 14 armoured personnel carriers.

Although the advances Ukraine has reported this month are its first substantial gains on the battlefield for seven months, Ukrainian forces have yet to push to the main defensive lines that Russia has had months to prepare.

'EVERYTHING IS STILL AHEAD' - UKRAINIAN COMMANDER

"I want to say that our main force has not been engaged in fighting yet, and we are now searching, probing for weak places in the enemy defences. Everything is still ahead," the Guardian quoted Oleksandr Syrskyi, the commander of Ukraine's ground forces, as saying in an interview with the British newspaper.

Moscow has sought to portray the Ukrainian counteroffensive as a failure. It says Kyiv's forces have suffered heavy losses, while Ukraine says Russia has lost many soldiers in heavy fighting since the counterattack began.

Reuters is unable to verify the situation on the battlefield but has reached two of the villages recaptured by Kyiv.

Ukraine has prepared new military units for its long-awaited counteroffensive, including 12 new brigades, but only three of them have been seen in combat so far. It has also received an array of weapons from its Western allies to help it take back swathes of territory occupied by Russia.

Presidential adviser Podolyak said that the time Ukraine had needed to persuade its Western partners to provide the necessary weapons had given the Russian military the opportunity to dig in and strengthen their defence lines.

"Breaking the Russian front today requires a reasonable and balanced approach. The life of a soldier is the most important value for Ukraine today," he said.

Zelenskiy, meanwhile, ordered the creation of a special commission to carry out an audit of heads of military draft offices in regions across Ukraine.

In his nightly video address, Zelenskiy said he had instructed commander in chief General Valery Zaluzhniy to remove the head of an office in the southern port of Odesa after media reports that the official owned property in Spain.

"It is very unpleasant, openly immoral and incorrect that this person remained in his position despite everything," he said.

(Reporting by Anna Pruchnicka, Writing by Olena Harmash, Editing by Timothy Heritage, Ron Popeski and Jonathan Oatis)