A Ukrainian writer and war crimes investigator wounded in a Russian missile strike on a restaurant last week has died, the freedom of expression group PEN said on Sunday.

Victoria Amelina, 37, was wounded when a Russian missile destroyed the Ria Pizza restaurant in the eastern city of Kramatorsk on Tuesday, killing 12 people, including children, and wounding dozens.

"With our greatest pain, we inform you that Ukrainian writer Victoria Amelina passed away on July 1st in Mechnikov Hospital in Dnipro," PEN Ukraine said in a statement on its Facebook page.

Amelina had been in the city with a delegation of Colombian journalists and writers, PEN said.

She was hospitalised with "multiple skull fractures", according to a surgeon treating the wounded.

Her novel "Dom's Dream Kingdom" was published in 2017 and shortlisted for the UNESCO City of Literature Prize and the European Union Prize for Literature, according to PEN.

Her poems, prose and essays have been translated into English, German, Polish and other languages.

Since 2022 she had been working to document Russian war crimes since the invasion and advocate for accountability, PEN said.

Ria Pizza in Kramatorsk -- one of the largest cities still under Ukrainian control in the east -- was popular with soldiers, journalists and aid workers.

Amelina's death takes the toll of the strike to 13. 

Ukraine recaptures 37sq km

Ukraine said on Monday its forces had recaptured 37 square kilometres (14 square miles) from Russian forces last week.

Kyiv announced a highly-anticipated counteroffensive several weeks ago after it accumulated stockpiles of Western arms and ammunition.

"Over the past week ... the area liberated (in the east) was increased by nine square kilometres," Deputy Defence Minister Ganna Malyar said, adding that Ukrainian forces had wrested another 28 sqaure kilometres in the south.

Ukrainian forces are coming up against heavily entrenched Russian defensive positions both along the southern and eastern fronts.

Malyar said Ukrainian troops were fighting "fierce" battles with Russian forces around the eastern flashpoint city of Bakhmut.

In the south, Ukrainian forces had "successes" along the front towards the Melitopol and Berdyansk sectors.

Ukraine's military commander-in-chief Valery Zaluzhny expressed frustration in an interview published Friday at the slow deliveries of weaponry promised by the West.