Russian troops fought to take complete control of the eastern industrial city of Sievierodonetsk on Wednesday as the United States said it will provide Ukraine with advanced rockets to help it force Moscow to negotiate an end to the war.

U.S. President Joe Biden said Washington would provide Ukraine with more advanced rocket systems and munitions so it can "more precisely strike key targets on the battlefield."

"We have moved quickly to send Ukraine a significant amount of weaponry and ammunition so it can fight on the battlefield and be in the strongest possible position at the negotiating table," Biden wrote in an opinion piece in the New York Times on Tuesday.

A senior Biden administration official said weaponry provided would include the M142 High Mobility Artillery Rocket System (HIMARS), which Ukraine's armed forces chief said a month ago was "crucial" to counter Russian missile attacks.

Addressing concerns the provision of such weapons could draw the United States into a direct conflict with Russia, senior administration officials said Kyiv gave "assurances" the missiles would not be used to strike inside Russia.

"These systems will be used by the Ukrainians to repel Russian advances on Ukrainian territory, but they will not be used on targets in Russian territory," the U.S. official told reporters.

The latest U.S. pledge of weapons for Ukraine - on top of billions of dollars worth of equipment already provided including anti-aircraft missiles and drones - came as Russia pressed its assault to seize the eastern Donbas region, having abandoned its earlier thrust toward Kyiv from the north.

Russian troops have now taken control of most of the eastern industrial city of Sievierodonetsk in Luhansk, one of two provinces in the Donbas, regional Governor Serhiy Gaidai on Tuesday.

Nearly all critical infrastructure in Sievierodonetsk had been destroyed and 60% of residential property damaged beyond repair, he added. Russian shelling had made it impossible to deliver aid or evacuate people.

A Russian victory in Sievierodonetsk and its twin city of Lysychansk across the Siverskyi Donets river would bring full control of Luhansk, one of two eastern provinces Moscow claims on behalf of separatists.

A pro-Moscow separatist leader said Russian proxies had advanced slower than expected to "maintain the city's infrastructure" and exercise caution around its chemical factories.

"We can say already that a third of Sievierodonetsk is already under our control," Russia's TASS state news agency quoted Leonid Pasechnik, the leader of the pro-Moscow Luhansk People's Republic, as saying.

Gaidai warned Sievierodonetsk residents not to leave bomb shelters due to what he said was a Russian air strike on a nitric acid tank.

The Luhansk People's Republic's police force said Ukraine's forces had damaged it. Ukraine and Russian-backed separatists traded accusations over a similar incident in April.

Jan Egeland, secretary general of the Norwegian Refugee Council aid agency which had long operated out of Sievierodonetsk, said he was "horrified" by its destruction.

Up to 12,000 civilians remain caught in crossfire, without sufficient access to water, food, medicine or electricity, Egeland said.

"The near-constant bombardment is forcing civilians to seek refuge in bomb shelters and basements, with only few precious opportunities for those trying to escape," he said.

WEAPONS PACKAGE

Kyiv says weapons sent by the United States and other countries since the start of the invasion have helped fend off Russian gains.

The high mobility artillery rocket systems are part of a $700 million weapons package expected to be unveiled by the United States on Wednesday.

The package also includes ammunition, counter fire radars, a number of air surveillance radars, additional Javelin anti-tank missiles, as well as anti-armour weapons, officials said.

Ukrainian President Volodymyr Zelenskiy has called for more weapons while lambasting the European Union, which agreed on Monday to cut imports of Russian oil, for not sanctioning energy from Moscow sooner.

The EU said it would ban imports of Russian oil by sea. Officials said that would halt two-thirds of Russia's oil exports to Europe at first, and 90% by the end of this year.

Responding to the EU oil embargo, Moscow widened its gas cuts to Europe in a move that pushed up prices and ratcheted up its economic battle with Brussels.

Putin launched his "special operation" in February to disarm and "denazify" Ukraine. Ukraine and its Western allies call this a baseless pretext for a war to seize territory.

Ukraine accuses Moscow of war crimes on a huge scale, flattening cities and killing and raping civilians. Russia denies the accusations.

Reuters