Russian attack kills at least 8 in Ukraine's Chernihiv

Three Russian missiles have slammed into a downtown area of the northern Ukrainian city of Chernihiv, hitting an eight-floor apartment building and killing at least eight people, officials say.

At least 18 people were injured in Tuesday morning attack, the city's acting mayor Oleksandr Lomako said.

Chernihiv lies some 150km north of the capital, Kyiv, near the border with Russia and Belarus, and has a population of about 250,000 people.

The latest Russian bombardment came as the war stretched into its third year and approached what could be a critical juncture as a lack of further military support from Ukraine's Western partners increasingly leaves it at the mercy of the Kremlin's bigger forces.

Ukrainian President Volodymyr Zelenskiy called for sufficient determination and support from Western partners following the attack.

"This would not have happened if Ukraine had received sufficient air defence equipment and if the world's determination to counter Russian terror had been sufficient," Zelenskiy said via the Telegram messaging app.

Through the winter months, Russia made no dramatic advance along the 1000km front line, focusing instead on attritional warfare.

However, Ukraine's shortage of artillery ammunition, troops and armoured vehicles has allowed the Russians to gradually push forward.

A crucial element for Ukraine is the hold-up in Washington of approval for an aid package that includes roughly $US60 billion ($A94 billion) for Ukraine.

House Speaker Mike Johnson said on Sunday he would try to move the package forward this week.

Ukraine's need is now acute, according to the Institute for the Study of War, a Washington-based think tank.

"The Russians are breaking out of positional warfare and beginning to restore maneuver to the battlefield because of the delays in the provision of US military assistance to Ukraine," the institute said in an assessment on Tuesday.

"Ukraine cannot hold the present lines now without the rapid resumption of US assistance, particularly air defense and artillery that only the US can provide rapidly and at scale," it said.

Ukrainian forces are digging in, building fortifications in anticipation of a major Russian offensive that Kyiv officials say could come as early as May.

Ukraine is using long-range drone and missile strikes behind Russian lines, which are designed to disrupt Moscow's war machine.

Russia's defence ministry said on Wednesday a Ukrainian drone was shot down over the Mordovia region, roughly 350km east of Moscow and 700km from the Ukrainian border.

Ukrainian drone developers have been extending the weapons' range and earlier in April struck a target some 1200km east of Ukraine.

AP and Reuters