A Russian missile tore through an outdoor market in eastern Ukraine on Wednesday, killing 17 people and wounding dozens, as US secretary of state Antony Blinken returned to the country with more than one billion dollars (£800 million) in new funding.

Mr Blinken’s fourth visit to the country was overshadowed by the strike in the city of Kostiantynivka, near the front line in the Donetsk region, that turned the marketplace into an inferno.

It was one of the deadliest bombardments of civilians in the 18-month-old war. In addition to the dead, at least 32 people were wounded.

“Those who know this place are well aware that it is a civilian area,” President Volodymyr Zelensky said at a news conference with the Danish prime minister in Kyiv.

“There aren’t any military units nearby. The strike was deliberate.”

Mr Blinken’s visit was aimed at assessing Ukraine’s three-month-old counteroffensive and signalling continued US support as some western allies express worries about Kyiv’s slow progress against invading Russian forces.

“We want to make sure that Ukraine has what it needs, not only to succeed in the counteroffensive but has what it needs for the long-term, to make sure that it has a strong deterrent,” Mr Blinken said.

“We’re also determined to continue to work with our partners as they build and rebuild a strong economy, strong democracy.”

About 175 million dollars (£140 million) of the total is in the form of weaponry to be provided from Pentagon stockpiles and another 100 million dollars (£80 million) is in the form of grants to allow the Ukrainians to purchase additional arms and equipment, according to the state department.

In addition to the military assistance, Mr Blinken announced nearly 805 million dollars (£644 million) in non-arms-related aid for Ukraine, including 300 million dollars (£240 million) for law enforcement, 206 million dollars (£165 million) in humanitarian aid, 203 million dollars (£162 million) to combat corruption and 90.5 million dollars (£72 million) for removing mines, the State Department said.

Russia Ukraine War
Rescue workers put out a fire after the rocket attack in Kostiantynivka (Evgeniy Maloletka/AP)

The package also includes a previously announced 5.4 million dollar (£4.3 million) transfer to Ukraine of frozen Russian oligarch assets.

Mr Blinken was to discuss other issues, including support for Ukraine’s economy, building on his June announcement of 1.3 billion dollars (£1 billion) to help Kyiv rebuild, with a focus on modernising its energy network, which was bombarded by Russia last winter.

Kremlin spokesman Dmitry Peskov said US assistance to Ukraine “can’t influence the course of the special military operation” – Moscow’s euphemism for the war.

Mr Blinken arrived in Kyiv for an overnight visit hours after Russia launched a missile attack on the city.

On the train to Kyiv, Mr Blinken met the Danish prime minister, Mette Frederiksen, who was also on an official visit, and thanked her for Denmark’s leadership in training Ukrainian pilots on F-16s and for promising to donate the fighter jets to Ukraine, according to state department spokesman Matthew Miller.

Washington officials said there will be discussions of alternative export routes for Ukrainian grain following Russia’s exit from the Black Sea Grain Initiative and its frequent attacks on port facilities in the Odesa region.

After arriving in Kyiv Mr Blinken laid a wreath at the city’s Berkovetske cemetery to commemorate Ukrainian troops killed defending the country.

He told foreign minister Dmytro Kuleba that the US has “seen good progress in the counteroffensive. It’s very heartening”.

In another meeting, Ukrainian prime minister Denys Shmyhal said Ukraine is grateful the US money is coming in the form of grants, not loans that would drive it into debt.

The trip was Mr Blinken’s fourth to Ukraine since the war began, including one brief excursion over the Polish-Ukrainian border in March 2022, just a month after the Russian invasion.

But it will be the first time America’s top diplomat spends the night in Kyiv since January 2022, before the invasion, in what US officials called another sign of American support.

Western analysts and military officials caution that the counteroffensive’s success is far from certain and that it could take years to rid Ukraine of entrenched, powerfully armed and skilled Russian troops.

Both sides will have to assess their supply shortages, with more battles of attrition likely over the winter.

A long war could stretch deep into next year and beyond, according to experts.