Russia said it had broken through two of Ukraine's fortified defence lines in the east of the country, while Western countries announced more military spending on Ukraine, including artillery rounds, as Kyiv warned of continued Russian attacks.

Bolstered by tens of thousands of reservists drafted in December, Russia has intensified attacks across southern and eastern Ukraine in recent weeks, and a major new offensive is widely anticipated as the first anniversary of its invasion nears.

The Russian Defence Ministry yesterday said Ukrainian forces had retreated in the face of Russian operations in the Luhansk region, although it gave no details and Reuters was not able to independently verify this and other battlefield reports.

"During the offensive ... the Ukrainian troops randomly retreated to a distance of up to 3km from the previously occupied lines," the ministry said on the Telegram messaging app.

"Even the more fortified second line of defence of the enemy could not hold the breakthrough of the Russian military."

The ministry did not specify in which part of the Luhansk region the offensive took place.

Later yesterday, Ukrainian deputy defence minister Hanna Malyar said Russian forces were mounting "round-the-clock" assaults on government positions, without specifying where.

"The situation is tense. Yes, it is difficult for us. But our fighters are not allowing the enemy to achieve their goals and are inflicting very serious losses," Malyar wrote on Telegram.

In Kyiv, the capital's military administration said six Russian balloons that may have contained reconnaissance equipment were shot down over the city yesterday after air raid sirens blared.

"The purpose of launching the balloons was possibly to detect and exhaust our air defences," it said on the Telegram messaging app. Russia did not immediately comment.

Russian onslaught on Bakhmut

Russia is also waging an artillery and ground onslaught on the city of Bakhmut in Donetsk province adjacent to Luhansk.

Near Bakhmut, Russian forces fired on more than 15 towns and villages, including the city itself, the General Staff of the Ukrainian Armed Forces said in its evening report.

They also trained tank, mortar and artillery fire on communities straddling the borders of Kharkiv and Luhansk region, it added.

Donetsk regional governor Pavlo Kyrylenko posted pictures and video of an apartment building littered with rubble that he said was destroyed in the city of Pokrovsk, southwest of Bakhmut, leaving three dead, 11 injured and one still in hospital in a serious condition.

Bakhmut's capture would give Russia a stepping stone to advance on two bigger cities, Kramatorsk and Sloviansk further west in Donetsk, which would revive Moscow's momentum ahead of the Feb 24 first anniversary of the invasion.

Nato secretary-general Jens Stoltenberg said alliance members were continuing to produce 155mm artillery rounds.

"So yes, things are happening, but we need to continue, we need to step up even more," he told reporters after a meeting of Nato defence ministers in Brussels.

Ukraine has received billions of dollars in military spending from Western countries. The United States has committed more than US$27.4 billion in security assistance to Ukraine since the conflict began in February last year.

European Union foreign policy chief Josep Borrell urged countries to join Germany in sending tanks.

US Defense Secretary Lloyd Austin said after the Brussels talks that Ukraine had a very good chance of taking and "exploiting" the initiative on the battlefield this year.

Austin said that for every new system Nato provides Kyiv, it will train troops on it.

Britain said it and other European nations would provide military equipment including spare parts for tanks and artillery ammunition to Ukraine via an international fund, with an initial package worth more than US$241 million.

Russia calls the invasion a "special military operation" against security threats, saying Nato shows hostility to Russia daily and is growing more involved in the conflict. Kyiv and its allies call Russia's actions a land grab.

On Jan 20, a senior US administration official said Washington was advising Ukraine to hold off with a major offensive until the latest supply of US weaponry is in place and training has been provided.

"We have to ensure that this spring it is truly felt that Ukraine is moving towards victory," Ukraine's President Volodymyr Zelenskiy wrote in an address yesterday.

- Reuters