After retreating from capturing the capital Kyiv early in the invasion, Russian forces using a campaign of devastating bombing now control large swaths of Ukraine's south and east, where pro-Russian separatists already control territory.

President Volodymyr Zelenskiy said Russia had used more than 3,000 cruise missiles to date and it was "impossible to count" the number of artillery and other strikes so far.

But Western deliveries of long-range arms are beginning to help Ukraine on the battlefield, with Kyiv citing a string of successful strikes carried out on 30 Russian logistics and ammunitions hubs, using several multiple launch rocket systems recently supplied by the West.

The strikes are causing havoc with Russian supply lines and have significantly reduced Russia's offensive capability, according to Ukraine's defence ministry.

Ukrainian officials say the new U.S.-made High Mobility Artillery Rocket Systems (HIMARS) they began receiving last month allow them to reach targets in Crimea, which was annexed by Russia in 2014, and other areas occupied by Russia.

"Good morning from HIMARS," Andriy Yermak, chief of staff to Ukraine's president, wrote on Telegram on Sunday alongside a video showing a large explosion which he said was another destroyed Russian ammunition depot in southern Ukraine.

RUSSIA INTENSIFIES OPERATIONS

Russian Defence Minister Sergei Shoigu on Saturday ordered military units to intensify operations to prevent Ukrainian strikes on areas held by Russia, according to a statement from the ministry.

Ukrainian military intelligence later reported shelling along the entire frontline and what it said was preparation for the next stage of the Russian offensive.

The Ukrainian military said Russia appeared to be regrouping units for an offensive toward Sloviansk, a symbolically important city held by Ukraine in the eastern region of Donetsk.

The British defence ministry said on Sunday that Russia was also reinforcing defences across areas it occupies in southern Ukraine after pressure from Ukrainian forces and pledges from Ukrainian leaders to drive Russia out.

Russian President Vladimir Putin launched his invasion on Feb. 24 calling it a "special military operation" to demilitarise its neighbour and rid it of dangerous nationalists.

Kyiv and the West say it was an imperialist land grab and attempt reconquer a country that broke free of Moscow's rule with the break-up of the Soviet Union in 1991.

The biggest conflict in Europe since World War Two has killed more than 5,000 people, forced more than 6 million to flee Ukraine and left 8 million internally displaced, says the United Nations.

Ukraine and the West say Russian forces are targeting civilians and been involved in war crimes, charges Moscow rejects.

Reuters