“Extremely fierce fighting” is raging in parts of Ukraine as Kiev forces continue their counter-offensive, the country’s deputy defense minister said, the BBC reported.

Hana Maliar wrote on Telegram that Ukrainian forces managed to advance near Bakhmut in the east and Zaporizhia in the south. But he admitted that Russian forces had begun to defend themselves fiercely in some areas. Her comments come after another night of Russian missile and drone strikes on cities across Ukraine.

Russia has stepped up its bombing campaign in recent weeks, despite President Vladimir Putin admitting that his forces are suffering from a shortage of missiles and drones. The latest wave included a relatively rare strike at the Black Sea port of Odessa.

Kiev’s long-awaited advance has been long overdue, and Ukrainian officials have accused Russia of increasing strikes in recent weeks to distract from the offensive. The Ukrainians say their troops have recaptured seven settlements and at least 90 square kilometers (35 square miles) since they launched their counteroffensive.

Ukraine’s deputy defense minister wrote on Telegram that Ukrainian troops had advanced around the town of Bakhmut, long the focus of a fierce and bloody battle with Russian forces. He said the soldiers advanced 200 meters to 500 meters into the town, as well as in the southern Zaporizhia province. However, the BBC points out that it cannot independently verify these claims.

She admitted that the counteroffensive had already led to some “extremely tough fighting” as Ukrainian forces try to break through well-entrenched Russian defense lines. Senior Western officials have warned that the Russians will not simply back down in the face of Ukrainian attacks, adding that Kiev’s gains will come at a cost. “Russian forces generally defended well from their well-prepared, defended positions and were falling back between tactical lines,” the sources said.

“This ‘maneuver defense approach’ is proving to be a challenge for the Ukrainians and has a cost. Therefore, the advance is currently slow,” they noted, adding that it was too early to tell how effective Ukraine’s offensive was. But they stressed that heavy casualties were expected, given that Russia had months to prepare defensive lines. “This would never be without risk,” they said. “What we’re seeing is not unexpected. It’s difficult and it’s a challenge for the Ukrainians. What we’ve seen, though, is that they’ve continued to push where they’ve been losing, and as a result they’ve continued to gain ground. So overall the business is going in the right direction ».

Both sides have reported increased casualties among their opponents, which cannot be independently verified. Wednesday night’s raids on the Black Sea port of Odessa in the east killed three people, Ukrainian officials said. Another 13 people were injured in the early morning attacks, which targeted a warehouse and damaged shops.

The southwestern city is vital for Ukraine’s grain exports via the Black Sea. Military commanders said Russia fired 10 missiles and 10 drones overnight, most of which were shot down by air defenses. They added that three of the four KH-22 missiles fired by a Russian warship in the Black Sea were shot down, with the last one managing to hit Odessa. Oleg Kiper, head of the region’s military administration, said the three dead were workers at the warehouse, which was used as a food storage center.

“There may be people under the rubble,” he added. More civilians were injured after the explosion and “air battle” damaged shops, restaurants – including a McDonald’s – and residential areas, Mr Kiper wrote on the Telegram.

Other strikes in the eastern cities of Kramatorsk and Kostiantynivka killed three more people and destroyed dozens of homes, Ukrainian authorities said. And six people – including four forest workers – were killed when Russia bombed a van in northeastern Ukraine on Tuesday. Ukrainian prosecutors said the attack took place near the village of Seredina-Buda, near the Russian border.

The UN nuclear chief has postponed a planned trip to the Zaporizhia nuclear power plant. Senior Ukrainian officials said Raphael Grossi had agreed to delay his trip until it was safer to travel. The head of the International Atomic Energy Agency (IAEA) said on Tuesday that he was “very concerned” that the plant could be caught in the crossfire of Ukraine’s counterattack.

Its officials also stressed their need to access a site near the plant to check water levels after the nearby reservoir that supplied cooling pools for the plant was affected by the destruction of the Kahovka Dam.

Meanwhile, in Moscow the State Duma [κοινοβούλιο] approved a new bill that allows the Defense Department to sign contracts with convicted criminals to fight in Ukraine. The new law will allow anyone who is being investigated for committing a crime, who has had his case heard in court or who has been convicted before the verdict comes into effect, to join the army.

People accused of sexual offences, treason, terrorism or extremism will be excluded from the law. The move – widely seen as Russia’s latest attempt to avoid a move to full conscription – seeks to fill the gaps left by rising casualties.

Ukraine said today it was making gradually increasing progress in its counter-offensive against Russian forces amid “extremely heavy” fighting.

In a post on the Telegram messaging app, Undersecretary of Defense Hana Maliar said the Ukrainian actions were “partially” successful.

During the previous day, Ukrainian troops advanced 200-500 meters in various areas near the city of Bakhmut, in eastern Ukraine, and 300-350 meters in the direction of Zaporizhia, in the southeastern part of the country, she said.

“Our troops are moving in the face of extremely heavy engagements and air and artillery superiority,” Maliar said.

She reported ongoing clashes near the village of Makarivka in the direction of Berdyansk, in southern Ukraine, and said fighting was raging in the Novodanilivka and Novopokrovsk regions in the direction of Mariupol.

A little later Maliar claimed that the Ukrainian losses are “disproportionately” less than those on the Russian side.

“In general, throughout the war, we had much fewer casualties,” he said via Telegram.

Speaking on Ukrainian television, he said that in the past week the number of enemy killed in the Khortytsia sector (east) of the front was 8.73 times greater than Ukrainian casualties. In the Tavria sector (south) it was 5.3 times greater).

On Tuesday, Russian President Vladimir Putin said Ukrainian casualties were ten times higher than Russian ones after Kiev’s counteroffensive began.

“Right now, we’re both on defense and offense, just in different areas (…) There’s a very serious matchup,” Maliar added. He also claimed that Russian forces have not advanced at all for over a week.

On Monday, Ukraine said it had recaptured seven settlements and its forces had advanced up to 6.5 kilometers deep, occupying 95 square kilometers of territory.