INTERNATIONAL: Ukrainian president Volodymyr Zelenskiy said on Tuesday 19th April the situation in Mariupol remains "as tough as possible", as Russia urged Ukrainians in the besieged port to lay down arms.

Russia gave Ukrainian fighters still holding out in Mariupol a fresh ultimatum to surrender on Wednesday as it pushed for a decisive victory in its new eastern offensive, while Western governments pledged more military help to Kyiv.

Thousands of Russian troops backed by artillery and rocket barrages were advancing in what Ukrainian officials have called the Battle of the Donbas.

Russia's nearly eight-week-long invasion has failed to capture any of Ukraine's largest cities, forcing Moscow to refocus in and around separatist regions.

The biggest attack on a European state since 1945 has, however, seen nearly 5 million people flee abroad and reduced cities to rubble.

Russia was hitting the Azovstal steel plant, the main remaining stronghold in Mariupol, with bunker-buster bombs, a Ukrainian presidential adviser said late on Tuesday. Reuters could not verify the details.

"The world watches the murder of children online and remains silent," adviser Mykhailo Podolyak wrote on Twitter.

After an earlier ultimatum to surrender lapsed and as midnight approached, Russia's defence ministry said not a single Ukrainian soldier had laid down their weapons and it renewed the proposal. Ukrainian commanders have vowed not to surrender.

"Russia's armed forces, based purely on humanitarian principles, again propose that the fighters of nationalist battalions and foreign mercenaries cease their military operations from 1400 Moscow time on 20th April and lay down arms," the Russian Defense Ministry said.

The United States, Canada and Britain said they would send more artillery weaponry, and the White House said new sanctions were being prepared.

^{PHOTO: UKRAINIAN PRESIDENT VOLODYMYR ZELENSKIY GIVING NIGHTLY ADDRESS, SPEAKING ABOUT FIGHTING IN MARIUPOL AND OTHER REGIONS IN UKRAINE}