KYIV, April 28 (Reuters) - The United States accused Russia on Thursday of planning to stage fake independence votes to justify its conquest of territory in Ukraine, as Russian forces stepped up their assault on the east.
More than two months into an invasion that has flattened cities but failed to capture the capital Kyiv, Russia is pursuing an offensive to seize two eastern provinces in a battle the West views as a decisive turning point in the war.
Although Russian troops were pushed out of northern Ukraine last month, they are heavily entrenched in the east, where Moscow-backed separatists have held some territory since 2014, and also hold a swathe of the south they seized in March.
The U.S. mission to the OSCE security body said the Kremlin might attempt "sham referenda" in southern and eastern areas it had captured since the Feb. 24 invasion, using "a well-worn playbook that steals from history’s darkest chapters".
"These falsified, illegitimate referenda will undoubtedly be accompanied by a wave of abuses against those who seek to oppose or undermine Moscow’s plans," the U.S. mission said. "The international community must make clear that any such referendum will never be recognised as legitimate."
Ukraine reported explosions overnight in the southern city of Kherson, the only regional capital Russia has captured so far since the invasion. Russian troops there had used tear gas and stun grenades on Wednesday to suppress pro-Ukrainian crowds, and were now shelling the entire surrounding region and attacking towards Mykolaiv and Kryvyi Rih, Ukrainian officials said.
Russian state media quoted an official from a self-styled pro-Russian "military-civilian commission" in Kherson on Thursday as saying the area would start using Russia's rouble currency from May 1.
Ukraine's general staff said Russia was also stepping up its main military assault in the east, where Moscow now aims to seize all of two provinces partially controlled by separatists.
"The enemy is increasing the pace of the offensive operation. The Russian occupiers are exerting intense fire in almost all directions," it said.
It identified Russia's main attack as near the towns of Slobozhanske and Donets, along a strategic frontline highway linking Ukraine's second largest city Kharkiv with the Russian-occupied city of Izyum. The Kharkiv regional governor said Russian forces were ratcheting up attacks from Izyum, but Ukrainian troops were holding their ground.
Kharkiv regional prosecutors said two civilians were killed and seven wounded in Russian shelling of the village of Pokotilovka on Thursday. Reuters could not independently verify the report. Russia denies targeting civilians.
RUSSIA TO NATO: 'DON'T TEST OUR PATIENCE'
U.S. President Joe Biden is expected to deliver remarks on Thursday in support of Ukrainians, the White House said.
Western countries have ramped up weapons deliveries to Ukraine in recent days as the fighting in the east has intensified. More than 40 countries met this week at a U.S. air base in Germany and pledged to send heavy arms such as artillery for what is expected to be a vast battle of opposing armies along a heavily fortified front line on open, flat terrain.
Washington now says it hopes Ukrainian forces can not only repel Russia's assault on the east, but also weaken its military so that it can no longer threaten neighbours. Russia says that amounts to NATO waging "proxy war" against it, and has made a number of threats this week of unspecified retaliation.
Russia has also reported what it says have been a series of Ukrainian strikes on Russian regions which border Ukraine, and has warned that such attacks risk significant escalation.
Ukraine has not directly accepted responsibility but says the incidents are payback, while Russia has taken umbrage at statements from NATO member Britain that it is legitimate for Ukraine to target Russian logistics.
"In the West, they are openly calling on Kyiv to attack Russia including with the use of weapons received from NATO countries," Russian Foreign Ministry spokeswoman Maria Zakharova told reporters in Moscow.
"I don't advise you to test our patience further."
British Defence Secretary Ben Wallace said that "having failed in nearly all his objectives", Russian President Putin was desperately seeking to cement Russian control of occupied territory, acting as a "cancerous growth" inside Ukraine.
When Russian forces were driven away from Kyiv last month, they left behind destroyed suburbs strewn with the bodies of hundreds of slain civilians in what Western countries call clear evidence of war crimes.
Moscow says, without evidence, that such signs of suspected atrocities are fake.
U.N. Secretary-General Antonio Guterres struck an emotional note during a visit to the formerly Russian-occupied Kyiv suburbs of Borodyanka and Bucha.
"I imagine my family in one of those homes, now destroyed and black. I see my granddaughters running away in panic, part of the family eventually killed," Guterres told reporters in Borodyanka, surrounded by scorched, windowless apartment blocks.
"Innocent civilians were living in these buildings, they were paying the highest price for a war which they have not contributed to at all."
Guterres met Putin in Moscow on Wednesday on a failed peace mission. Russia rebuffed the U.N. chief's offer to help evacuate Mariupol, the besieged port that has been scene of the war's bloodiest fighting and worst humanitarian catastrophe.
Ukrainian troops are still holed up in a giant steel works in Mariupol. Putin claimed victory in the city last week, ordering the steel works blockaded. Kyiv says 100,000 civilians are still trapped in the city's ruins.
"As long as we're here and holding the defence... the city is not theirs," Captain Sviatoslav Palamar, deputy commander of Ukraine's Azov Regiment, told Reuters in video link from an undisclosed location beneath the huge factory.
Over 5 million refugees have fled abroad since Russia launched its "special military operation" in Ukraine with the stated aim to disarm its neighbour and defeat nationalists. The West calls this a bogus pretext for a war to seize territory.
