A Russian strike killed more than a dozen people, including a child, in a market in the frontline in east Ukraine, in an attack that President Volodymyr Zelensky described as "heinous evil".

The projectiles ripped into the centre of Kostiantynivka, a town of nearly 70,000 people in the Donetsk region hours after America's top diplomat arrived in Kyiv to announce new aid.

Ukraine's newly appointed defence minister meanwhile vowed to liberate "every centimetre" of territory occupied by Russia in his first comments in the post Wednesday.

Rescue workers picked through the debris and carried some of the nearly 30 wounded for treatment past charred vehicles and kiosks torn to pieces in the blast, according to images distributed by officials.

"Sixteen people have been killed, including one child," Prime Minister Denys Shmygal said on social media following the strike in the market about 20 kilometres (12 miles) from the front line.

The industrial Donetsk region has been partially controlled by Kremlin-backed separatists since 2014 and Russia claimed to have annexed in late last year.

"Anyone in the world who is still dealing with anything Russian simply ignores this reality. Heinous evil. Brazen wickedness. Utter inhumanity," Zelensky said.

The attack came as US Secretary of State Antony Blinken's visited Ukraine, with Washington set to unveil more than $1 billion in fresh aid to battle Russia.

During a meeting with Foreign Minister Dmytro Kuleba, Blinken reiterated Washington's support for Kyiv in its fight to liberate territory in the south and east.

- 'Good progress' -

"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," he told Kuleba.

Blinken is expected to announce "more than a billion dollars in new US funding for Ukraine," according to a senior State Department official.

The Kremlin dismissed Blinken's Kyiv visit, arguing US aid would not "influence the course of the special military operation" -- Moscow's term for its offensive.

Kremlin spokesman Dmitry Peskov accused Washington of wanting to "keep Ukraine in a state of war, to wage this war till the last Ukrainian".

Kyiv's army has said it is pressing on with "offensive operations" towards eastern Ukraine's war-battered town of Bakhmut -- which fell to Russian forces in May -- and the southern Moscow-occupied city of Melitopol.

It said troops had been "successful" near the southern villages of Robotyne and Novoprokopivka.

Blinken told Kuleba that "we've seen some good progress."

The US has supplied key weaponry to Ukraine that allowed it to go on the advance this summer.

But Ukraine has in recent weeks become increasingly frustrated with criticism that the counter-offensive has been to slow.

Russia, meanwhile, said Wednesday it had "improved its tactical position" near the north-western city of Kupiansk, where it has led a local offensive for weeks.

It also hit Ukraine's south-western Odesa region, near the border with Romania, with drone attacks overnight, killing one person.

- 'Everything possible and impossible' -

In what was hailed as a historic move, Ukrainian lawmakers approved the nomination of Crimean Tatar Rustem Umerov as Kyiv's new wartime defence minister Wednesday.

Crimean Tatars are an ethnic minority hailing from the Black Sea peninsula, which was annexed by Russia in 2014.

"I will do everything possible and impossible for the victory of Ukraine -- when we liberate every centimetre of our country and every one of our people," he said in a post on social media.

The 41-year-old businessman has been involved in prisoner exchange negotiations involving Saudi Arabia and grain export talks with Turkey and the United Nations.

"We will definitely return everyone who, unfortunately, are temporarily in captivity," he said as he took up his post.

"Children, prisoners of war, political prisoners, civlians... are waiting for us."

Zelensky had nominated Umerov as new defence minister after the resignation of Oleksiy Reznikov, calling for "new approaches" and in the wake of several corruption scandals in the ministry.

"It is the highest state post ever held by a Tatar (from Crimea)," Sergiy Leshchenko, an advisor to the presidential administration, told AFP.

- Danish PM visits -

A string of Western leaders has visited Kyiv during the war, pledging support against Russian forces.

Denmark's Prime Minister Mette Frederiksen was the latest to travel to the Ukrainian capital Wednesday, after pledging to supply Ukraine with 19 F-16 fighter jets.

Denmark and the Netherlands last month announced they would provide the advanced jets to strengthen Kyiv's Soviet-era air force.

State Department spokesman Matthew Millar said Blinken met Frederiksen as they travelled to Ukraine and thanked her for "its decision to donate F-16 jets to Ukraine."

Frederiksen also visited Bucha, the Kyiv suburb where civilian corpses were discovered after a Russian retreat at the start of Moscow's invasion last year.