Russian troops have pressed closer to the centre of a factory city in their drive to grab a swathe of eastern Ukraine, while the United States says it will supply advanced rockets to Kyiv to help it force Moscow to negotiate an end to the war.

Ukraine’s General Staff on Wednesday said Russian forces – 98 days into their invasion – were pounding infrastructure in eastern and southern regions including the symbolically important industrial city of Sievierodonetsk, which they entered on May 27.

It has been the main focus of their ground offensive for several weeks.

Sievierodonetsk is a Soviet-era city that houses a large chemical factory.

According to the local governor, a Russian airstrike hit a large chemical plant in the city on Tuesday, blowing up a tank of toxic nitric acid.

Russia “attacked the Azot factory from a plane, resulting on the release of toxic substances,” Governor Serhiy Gaidai said, urging residents to remain inside. Reuters could not independently confirm the cause of the incident.

US President Joe Biden announced the supply of precision rocket systems and munitions that could strike at long-range Russian targets, part of a $US700 million ($973 million) weapons package expected to be unveiled on Wednesday.

“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,” Mr Biden wrote in an opinion piece in the New York Times.

A senior Biden administration official said the new supplies, which comes on top of billions of dollars worth of equipment such as drones and anti-aircraft missiles, included the M142 High Mobility Artillery Rocket System (HIMARS), which Kyiv has said is “crucial” to counter Russian missile attacks.

Ukraine welcomed the West’s supply of weapons, which has included M777 howitzers deployed along the frontline in the Luhansk region that includes Sieverodonetsk.

Addressing concerns that weapons such as HIMARS could draw the United States into direct conflict, senior administration officials said Ukraine had given assurances the missiles would not strike inside Russia.

Russia, however, warned of an increased risk of direct confrontation with the US. Deputy Foreign Minister Sergei Ryabkov told state news agency RIA Novosti that Moscow viewed the development “extremely negatively.”

Shortly after the US decision was announced, the Russian defence ministry said Russia’s nuclear forces were holding drills in the Ivanovo province, north-east of Moscow, the Interfax news agency reported.

Some 1000 servicemen were exercising in intense manoeuvres using more than 100 vehicles including Yars intercontinental ballistic missile launchers, it cited the ministry as saying.

There was no mention of the US decision to supply new weapons in the Interfax report.

Russia has also completed testing of its hypersonic Zircon cruise missile and will deploy it by the end of the year on a new frigate of its Northern Fleet, a senior military officer said on Wednesday.

Ukraine’s General Staff said Russian forces continued to pound northern, southern and eastern districts of Sievierodonetsk.

If Russia captures the city and its smaller twin Lysychansk on the west bank of the Siverskyi Donets river, it will hold all of Luhansk, one of two provinces in the eastern Donbas region that Moscow claims on behalf of separatists and a key war aim of President Vladimir Putin.

The new US package 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 Zelensky 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 Russia 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 per cent by the end of this year.

Putin launched what he calls a special military operation on February 24 to disarm and “denazify” Ukraine.

Ukraine and its Western allies call this a baseless pretext for a war of aggression.

-Reuters