(AFP) - Russian President Vladimir Putin made a surprise trip to Mariupol, the Kremlin said Sunday, his first visit to territory captured from Ukraine since the start of Moscow's invasion.

Just hours after Putin visited Crimea to mark the ninth anniversary of the peninsula's annexation, video distributed by the Kremlin showed him landing by helicopter in Mariupol, the port city that Moscow captured after a long siege last spring.

The visit triggered an angry reaction from Ukraine, with a presidential aide blasting its "cynicism" and "lack of remorse".

The Russian leader took a tour of the city and was seen driving a car. The Kremlin said he visited a rebuilt musical theatre and followed the presentation of a report on reconstruction work.

"We're praying for you," a resident told Putin, referring to the city as "a little piece of paradise", according to images broadcast by Russian state TV, showing the visit took place at night.

Kremlin spokesman Dmitry Peskov told reporters the visit was "spontaneous", adding that Putin's movements around the city and his meeting with locals were not planned.

He added that the visit took place "very late" on Saturday and in the early hours of Sunday.

It was Putin's first trip to the eastern Donbas region since he launched the invasion in February 2022, and comes almost a year after Moscow announced the capture of Mariupol after a campaign that saw the destruction of the Azovstal steel works, the last holdout of Ukrainian forces in the strategic port city.

- 'Lack of remorse' -

Mariupol was left devastated after Moscow relentlessly bombarded the city on the shores of the Sea of Azov and subjected it to a brutal siege.

"The criminal always returns to the crime scene... the murderer of thousands of Mariupol families came to admire the ruins of the city and (its) graves. Cynicism and lack of remorse," Ukrainian presidential aide Mykhaylo Podolyak said on Twitter.

Ukraine's defence ministry said on Twitter Putin visited the city at night "as befits a thief".

"He watched the 'rebuilding of the city'... at night. Probably in order not to see the city, killed by his 'liberation', in the light of day," the exiled Mariupol city council said on its Telegram account.

The visit comes ahead of a trip to Moscow this week by Chinese President Xi Jinping, widely seen as a diplomatic coup for Putin.

Beijing, a strategic ally of Moscow, has touted the trip as a "visit for peace" as it seeks to play mediator in the Ukraine conflict.

China has sought to position itself as a neutral party, urging Moscow and Kyiv to open negotiations.

But Western leaders have repeatedly criticised Beijing for failing to condemn Russia's offensive, accusing it of providing Moscow with diplomatic cover for its campaign.

Putin also met army chiefs including the chief of the general staff, Valery Gerasimov, in the southern Russian city of Rostov-on-Don near the border with Ukraine, the Kremlin said.

He also made an unannounced visit to Crimea on Saturday, with Russian state TV showing him visiting the Black Sea port city of Sevastopol accompanied by the local Moscow-appointed governor Mikhail Razvozhayev.

- 'Void' ICC warrant -

Russia annexed Crimea in 2014 following a referendum that was not recognised by Kyiv and the international community.

The weekend visits came after the International Criminal Court, based in The Hague, issued an arrest warrant for Putin over Russia's alleged deportation of thousands of Ukrainian children during the conflict.

Kyiv says more than 16,000 Ukrainian children have been deported to Russia since the start of the conflict, many of them placed in institutions and foster homes.

ICC prosecutor Karim Khan told AFP that Putin was now liable for arrest if he set foot in any of the court's more than 120 member states.

The 70-year-old Russian leader has not commented publicly on the warrant but the Kremlin dismissed its validity as "void" since Russia did not recognise the ICC's jurisdiction.

In Ankara, Turkish President Recep Tayyip Erdogan said Saturday Moscow and Kyiv had agreed to extend a deal that allows Ukraine, a major grain exporter, to resume exports after its Black Sea ports were blocked by Russian warships.

However, there is still a disagreement over the terms, with Ukraine saying the deal had been extended for 120 days and Russia saying it was prolonged by 60 days.

Fighting on the ground is concentrated in the eastern Donetsk region of Ukraine, particularly the city of Bakhmut.

Russia last autumn announced the annexation of Donetsk along with three other Ukrainian territories -- Lugansk, Kherson and Zaporizhzhia -- despite not fulling controlling them.

Russian shelling on Sunday killed three people and injured two others in the village of Kamianske in the southern Zaporizhzhia region, the regional administration said.

© Agence France-Presse