* Ukraine wants more artillery for battle in the east

* Mariupol mayor fears thousands may die from cholera there

* Food shortages caused by war could lead to hunger globally -U.N.

KYIV, June 11

Ukraine pleaded to Western countries for faster deliveries of weapons as better-armed Russian forces pounded the east of the country, and for humanitarian support to combat growing outbreaks of deadly diseases.

In Sievierodonetsk, the small city that has become the focus of Russia's advance in eastern Ukraine and one of the bloodiest flashpoints in a war well into its fourth month, further heavy fighting was reported.

The war in the east, where Russia is focussing its attention, is now primarily an artillery battle in which Kyiv is severely outgunned, Ukrainian officials say. That means the tide of events could be turned only if Washington and others fulfil promises to send more and better weaponry, including rocket systems.

'This is an artillery war now,' Vadym Skibitsky, Ukraine's deputy head of military intelligence, told Britain's Guardian newspaper.

'Everything now depends on what (the West) gives us. Ukraine has one artillery piece to 10 to 15 Russian artillery pieces.'

Germany, among the largest suppliers of weapons since Russia invaded but criticised for being slow to supply the heavy weaponry Kyiv says it needs, plans to revise its rules on arms exports to make it easier to arm democracies like Ukraine, Der Spiegel reported on Friday. Read full story

To the south, the mayor of Mariupol - reduced to ruins by a Russian siege – said sanitation systems were broken and corpses were rotting in the streets.

'There is an outbreak of dysentery and cholera,' Vadym Boichenko told national television. 'The war which took over 20,000 residents ... unfortunately, with these infection outbreaks, will claim thousands more Mariupolites,' he said, adding some wells had been contaminated by corpses.

Boichenko called on the United Nations and the International Committee of the Red Cross to establish a humanitarian corridor to allow remaining residents to leave the city, which is now under Russian control.

In a snapshot of the war's wider impact, the U.N. food agency said reduced exports of wheat and other food commodities from Ukraine and Russia could inflict chronic hunger on up to 19 million more people globally over the next year.

BATTLE FOR SIEVIERODONETSK

Russia hopes to capture all of the eastern province of Luhansk, which it demands Ukraine cede to separatists along with neighbouring Donetsk. The two provinces make up the Donbas region, where Moscow has backed a revolt by separatist proxies since 2014.

To that end, the Kremlin has concentrated its forces into a battle for Sievierodonetsk, which is in Luhansk.

Ukrainian troops have largely pulled out of the city's residential areas but have not yielded their foothold on the east bank of the Siverskiy Donets River. Russian forces are also pushing from the north and south to try to encircle the Ukrainians, but have made limited progress.

Ukraine's army command said on Saturday that Russia troops had secured positions in two communities near Sievierodonetsk, while Serhiy Gaidai, the Luhansk governor, said Russians were in control of 'most' of the city.

Gaidai said the main road from Bakhmut to Lysychansk/Sievierodonetsk was being constantly shelled but there had been no changes in positions.

Britain's Ministry of Defence said the Russians had not made advances into the south of Sievierodonetsk.

'Intense street to street fighting is ongoing and both sides are likely suffering high numbers of casualties,' the ministry said in an intelligence update posted on Twitter.

Ukraine said Russia had regrouped troops and replenished ammunition and fuel supplies in preparation for offensives in Sloviansk and Siversk, cities in the Donetsk region.

'HAPPY TOWNS' IN RUINS

President Volodymyr Zelenskiy said Russia was trying to 'break every town in the Donbas.'

'Sievierodonetsk, Lysychansk, Bakhmut, Sloviansk, many, many others,' he said in his nightly address. 'All these ruins were once happy towns.'

Both sides say they have inflicted mass casualties. Reuters could not immediately verify battlefield reports.

Zelenskiy adviser Oleksiy Arestovych estimated the Russian army is losing on average five to six times as many fighters as the Ukrainian side.

Asked in a social media interview whether that suggested the Ukrainian army had lost up to 10,000 fighters in the first 100 days of the war, Arestovych said, 'Yes, something like that.'

Russian President Vladimir Putin launched what he terms his 'special military operation' in Ukraine on Feb. 24, saying his aim was to disarm and 'denazify' Russia's neighbour. Kyiv and its allies call it an unprovoked war of aggression to capture territory.

Weapons experts from France are helping their Ukrainian counterparts collect evidence of possible Russian war crimes in the northern region of Chernihiv, Ukraine's prosecutor general said. Russia denies targeting civilians. Read full story

U.S. Defense Secretary Lloyd Austin on Saturday reinforced Washington's commitment to the region in light of Russia's actions.

'Russia's invasion of Ukraine is what happens when oppressors trample the rules that protect us all,' Austin told an Asian security forum in Singapore. 'It's a preview of a possible world of chaos and turmoil that none of us would want to live in.' Read full story

Zelenskiy is expected to give a virtual address to the conference from 0800 GMT.