KYIV — Russia escalated its attacks on Ukraine, unleashing a campaign of violence in urban areas as its forces closed in on the main cities. The long military convoy outside Kyiv continues to advance slowly on the capital.

Ukraine's second city Kharkiv saw more civilian casualties as Russian forces intensified their bombardment, hitting residential areas.

Russia says it plans to target key security infrastructure in the capital, warning residents to flee. Moscow has denied targeting civilian areas, despite mounting evidence to the contrary.

An intensified assault continued on Kharkiv overnight, with reports of Russian artillery strikes and airborne troops landing in Ukraine's largest city.

In Kherson, the Russian troops took control of the railway station and the port during the night after already controlling the entrances to the city.

Russian forces pressed their assault on other towns and cities across the country, including the strategic port of Mariupol in the south.

Belarusian troops were put on alert and could join the invasion shortly as the Ukrainian intelligence noticed "significant activity" of Minsk aircraft and supplies near the border.

Human Rights Watch said it documented a cluster bomb attack outside a hospital in Ukraine's east in recent days. Local residents also reported the use of the weapons in Kharkiv and the village of Kiyanka. The Kremlin denied using cluster bombs.

A senior US defence official described the long Russian army convoy heading to Kyiv as "bogged down", saying Russia appeared to be pausing and regrouping to evaluate how to retake the momentum in the fighting.

Overall, the Russian military has been stalled by fierce resistance on the ground and a surprising inability to completely dominate Ukraine's airspace.

The UN says more than 660,000 refugees have fled Ukraine in six days and numbers are growing "exponentially".

Russia's largest bank, Sberbank Group, said it was pulling out of the European market after being hit by massive financial sanctions in retaliation for Moscow's invasion of Ukraine.

"In the current situation, Sberbank has decided to withdraw from the European market. The group's subsidiary banks are facing abnormal outflows of funds and threats to the safety of their employees and offices," the group said in a statement on Wednesday, quoted by Russian state news agencies.

Ukraine's defence ministry said overnight it was concerned of an attack by Belarus "in the near future".

"Belarusian troops have been put on alert and are concentrating in the areas closest to the border with Ukraine," the ministry said in a statement on Facebook.

Ukrainian intelligence noted "significant activity" of aircraft in the border area on Tuesday and convoys of vehicles carrying food and ammunition were observed there, the statement said.

In view of these movements, Belarus "could probably support Russian invaders [...] in the near future," the ministry warned.

Missile attacks against military and civilian targets in Ukraine have been "systematically" launched from Belarusian territory since the Russian invasion began on 24 February, it added.

Russian military equipment was reported to be stationed in front of the Regional State Administration building in Kherson, and explosions were heard in the city on Wednesday, according to local media.

The Russian forces took control of the railway station and the port during the night, according to Mayor Igor Kolykhayev.

In Borodianka, 50 km from Kyiv, Russian airstrikes destroyed two residential buildings on Tuesday, Ukraine's first deputy foreign minister Eminé Djaparova stated, sharing a video of the buildings partially in ruins, with flats in flames.

Russian airborne troops landed in Kharkiv overnight, the Ukrainian military said Wednesday, reporting ongoing fighting in Ukraine's second-largest city in the east.

"A fight is underway between the invaders and Ukrainians," a statement on Telegram said.

Anton Gerashchenko, an adviser to the Ukrainian interior minister, said a fire broke out on Wednesday in the barracks of a flight school in Kharkiv after an airstrike.

"Practically, there is no area left in Kharkiv where an artillery shell has not yet hit," he said, quoted in a statement on Telegram.

Kharkiv, a city of 1.4 million people near the border with Russia, was targeted by several bombings on Tuesday, which killed at least ten people and injured more than 20, according to local authorities.

If his Russian counterpart were not made to “pay a price” for the invasion, the aggression would not stop with one country, the US President Joe Biden warned on early Wednesday.

In his first State of the Union address, Biden highlighted the resolve of a reinvigorated Western alliance that has worked to rearm the Ukrainian military and adopt tough sanctions, which he said have left Putin ”isolated in the world more than he has ever been”.

Biden also announced that the US is banning Russian flights from its airspace in retaliation for the invasion of Ukraine, following similar moves by the European Union and Canada.

Biden devoted the first 12 minutes of his Tuesday evening address to Ukraine, with lawmakers of both parties repeatedly rising to their feet and applauding as he praised the bravery of Ukraine’s people and condemned Putin’s assault.

The 193-member General Assembly scheduled a vote for Wednesday afternoon after hearing 120 speeches on a UN resolution demanding an immediate halt to Moscow's offensive and withdrawal of all Russian troops.

As of late Tuesday, the resolution had 94 co-sponsors, including several surprises to UN diplomats — Afghanistan, where the Taliban ousted the elected government last August, and Myanmar, where the military overthrew the elected government led by Aung San Suu Kyi in February 2021.

Russia did have a few supporters at the UN General Assembly's emergency session, including Cuba and North Korea. Some countries took no position on the draft resolution, such as Surinam and South Africa, which urged compromise and diplomacy to find a lasting solution to the crisis.

Unlike Security Council resolutions, General Assembly resolutions are not legally binding, but they do have clout in reflecting international opinion. — Agencies