Ukraine has hit back at doubters over the progress of its summer counteroffensive, insisting recent modest gains against Russian occupiers were merely a “preview” of a much bigger push to come.

Oleksiy Reznikov, Ukraine’s defence minister, told the Financial Times that the liberation of a group of villages under Russian occupation in recent weeks was “not the main event” in Kyiv’s planned attack.

“When it happens, you will all see it . . . Everyone will see everything,” said Reznikov, brushing aside media coverage of slow progress against well-fortified Russian positions.

He confirmed that Ukraine’s main troop reserves, including most brigades recently trained in the west and equipped with modern Nato tanks and armoured vehicles, have yet to be used in the operation.

Reznikov argued the past weekend’s insurrection by the Wagner paramilitary group had laid bare the fundamental weakness of Vladimir Putin’s regime in Moscow. “It’s like a snowball,” he said, referring to the regime’s self-destructive traits. “The bigger it gets, the faster it rolls.”

But he cautioned against Ukraine banking on further “mutinies and riots” in Russia for battlefield success, saying there were no immediate signs of a collapse in morale. “Once it gets hot, we’ll see how resilient they are,” he said pointing to future counteroffensive operations.

“We need to trust in our security and defence forces as well as our partners providing weapons,” he added, stressing these factors were more “predictable” than the situation in Russia.

A former Soviet paratrooper who claims parachuting as a hobby, Reznikov said Ukraine’s army continued to impose heavy losses on Russian troops, with “degradation as a tool and the liberation of Ukrainian lands as the goal”.

Ukraine’s counteroffensive has so far recaptured about 300 square kilometres from Russia, according to the UK ministry of defence, double what Kyiv has officially announced. Even so, Ukraine’s president Volodymyr Zelenskyy has acknowledged the gains are “slower than desired”.

Reznikov said Ukraine’s forces had made “certain gains” that the general staff had not made public to avoid exposing troops. “Sometimes the Russians do not report to their leadership that they have lost a certain area or territory. They are afraid to report further to their superiors,” he said.

While the insurrection led by the Russian warlord Yevgeny Prigozhin had yet to change the calculus on the battlefield, Reznikov said it offered a “vivid illustration” of Russia’s vulnerabilities. “This helps the west realise that they are investing in Ukraine for a reason, that Ukraine’s victory is absolutely real and coming soon,” he said.

Reznikov expressed hope that the mayhem in Russia would encourage western capitals to further boost the supply of weapons to help Kyiv towards victory.

As Ukraine’s top negotiator with western counterparts on arms supplies, Reznikov has formed strong relationships with western counterparts including US defence secretary Lloyd Austin, who routinely refers to his Ukrainian colleague as “my close friend”.

Reznikov renewed Kyiv’s appeal to Nato, whose leaders will meet in Vilnius in July, to advance Ukraine’s bid to join the alliance although he acknowledged it would not be offered membership at this stage of the war.

“We are aware that during the hot phase, it is unlikely to make a unanimous political decision. But a clear signal, a clear design.”

Ukraine was the only country in the world that had battlefield experience “of restraining the Russians . . and [of] beginning to beat them with Nato weapons”, Reznikov said.

“What other argument is needed to invite Ukraine to Nato?”

Ukrainian forces are currently involved in shaping operations to test Russian lines, which Russia has heavily fortified with multiple layers of troops, minefields and trenches. Analysts say the multiple points of attack are designed to keep Russia guessing about where the main attack would be launched.

Reznikov cautioned that the operation would contrast with last year’s stunning rout of Russian forces in Kyiv, the northeastern Kharkiv region and the southern city of Kherson. “You can’t expect a miracle in every operation.”