RUSSIAN forces are carrying out a campaign of “terror” in Ukraine as Vladimir Putin’s troops lay siege to three major cities and step up attacks on residential areas.

“Nobody will forgive. Nobody will forget,” Ukraine’s president Volodymyr Zelensky vowed after the bloodshed on the central square in Kharkiv, where airborne Russian troops have landed.

A 40-mile convoy of hundreds of Russian tanks and other vehicles advanced slowly on Kyiv, the capital city of nearly three million people.

Russian troops have been spotted in the centre of Kherson, in southern Ukraine. Russia's defence ministry claimed on Wednesday that it has captured the port city, according to RIA news agency.

The Russians also pressed their assault on other towns and cities, including the strategic ports of Odesa and Mariupol in the south.

Day six of the biggest ground war in Europe since the Second World War found Russia increasingly isolated, beset by the sanctions that have thrown its economy into turmoil and left the country practically friendless, apart from a few nations like China, Belarus and North Korea.

The National: Ukrainian president Volodymyr ZelenskyUkrainian president Volodymyr Zelensky

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As the fighting in Ukraine raged, the death toll remained unclear.

One senior Western intelligence official estimated that more than 5000 Russian soldiers had been captured or killed. Ukraine gave no overall estimate of troop losses.

The UN human rights office said it has recorded 136 civilian deaths. The real toll is believed to be far higher.

The UK Ministry of Defence said overnight it had seen an increase in Russian air and artillery strikes on populated urban areas over the past two days. It also said three cities – Kharkiv, Kherson and Mariupol – were encircled by Russian forces.

Many military experts worry that Russia may be shifting tactics. Moscow’s strategy in Chechnya and Syria was to use artillery and air bombardments to pulverize cities and crush fighters’ resolve.

Ukrainian authorities said five people were killed in the attack on the TV tower, which is near central Kyiv and a short walk from numerous apartment buildings. A TV control room and power substation were hit, and at least some Ukrainian channels briefly stopped broadcasting, officials said.

The bombing came after Russia announced it would target transmission facilities used by Ukraine’s intelligence agency. It urged people living near such places to leave their homes.

Zelensky’s office also reported a missile attack on the site of the Babi Yar Holocaust memorial, near the tower.

A spokesman for the memorial said a Jewish cemetery at the site, where Nazi occupiers killed more than 33,000 Jews over two days in 1941, was damaged, but the extent would not be clear until daylight.

In Kharkiv, with a population of about 1.5 million, at least six people were killed when the region’s Soviet-era administrative building on Freedom Square was hit with what was believed to be a missile.

The Slovenian foreign ministry said its consulate in Kharkiv, located in another large building on the square, was destroyed in the attack.

The attack on Freedom Square, Ukraine’s largest plaza, and the nucleus of public life in the city, was seen by many Ukrainians as brazen evidence that the Russian invasion was not just about hitting military targets but also about breaking their spirit.

The bombardment blew out windows and walls of buildings that ring the massive square, which was piled high with debris and dust. Inside one building, chunks of plaster were scattered, and doors, ripped from their hinges, lay across hallways.

“People are under the ruins. We have pulled out bodies,” said Yevhen Vasylenko, an emergency official.

Zelensky called the attack “frank, undisguised terror” and a war crime. “This is state terrorism of the Russian Federation,” he said.

In an emotional appeal to the European Parliament later, Zelensky said: “We are fighting also to be equal members of Europe. I believe that today we are showing everybody that is what we are.”

Another Russian airstrike hit a residential area in the city of Zhytomyr, the town’s mayor said.

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Ukraine’s emergency services said Tuesday’s strike killed at least two people, set three homes on fire and broke the windows in a nearby hospital.

About 85 miles west of Kyiv, Zhytomyr is the home of the elite 95th Air Assault Brigade, which may have been the intended target.

Zelensky said 16 children had been killed around Ukraine on Monday, and he mocked Russia’s claim that it is going after only military targets.

“Where are the children? What kind of military factories do they work at? What tanks are they going at?” Zelensky said.

Human Rights Watch said it documented a cluster bomb attack outside a hospital in Ukraine’s east in recent days. Residents also reported the use of such weapons in Kharkiv and Kiyanka villiage.

The Kremlin denied using cluster bombs.

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Cluster bombs shoot smaller “bomblets” over a large area, many of which fail to explode until long after they’ve been dropped. If their use is confirmed, that would represent a new level of brutality in the war and could lead to further isolation of Russia.

The first talks between Russia and Ukraine since the invasion were held on Monday, but ended with only an agreement to talk again. On Tuesday, Zelensky said Russia should stop bombing first.

“As for dialogue, I think yes, but stop bombarding people first and start negotiating afterwards,“ he told CNN.

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Inside Russia, a top radio station critical of the Kremlin was taken off the air after authorities threatened to shut it down over its coverage of the invasion. Among other things, the Kremlin is not allowing the fighting to be referred to as an “invasion” or “war”.

“It is a nightmare, and it seizes you from the inside very strongly. This cannot be explained with words,” said Kharkiv resident Ekaterina Babenko, taking shelter in a basement with neighbours for a fifth straight day. “We have small children, elderly people, and frankly speaking it is very frightening.”

Ukraine’s defence ministry also said on Tuesday it has evidence that Belarus, a Russian ally, is preparing to send troops into Ukraine, while oil prices surged more than $5 (£3.75) per barrel after a release of supplies failed to calm markets.

In the US, President Joe Biden in his first State of the Union address that the US was closing airspace to Russian planes and vowed to seize the yachts and apartments of Russian oligarchs.

Leading Russian bank Sberbank also announced on Wednesday that it is pulling out of European markets amid tightening Western sanctions.

The bank said its subsidiaries in Europe were facing an “abnormal outflow of funds and a threat to the safety of employees and branches”, according to Russian news agencies.

BBC Studios, meanwhile, revealed on Tuesday that it was halting all content licensing with its Russian customers over the invasion of Ukraine. ITV has also stopped working with Russian customers because of the conflict.