A week after launching its invasion of Ukraine, Russia said its forces took control the first sizable city on Wednesday, seizing Kherson, in the south, as fighting raged around the country and Western nations tightened an economic noose around Russia.

More than half a million Ukrainians have fled the fighting since Russian President Vladimir Putin ordered a full-scale invasion of his southern neighbour nearly a week ago.

Russian bombardments of Ukrainian cities continued, with video posted on social media showing heavily damaged buildings around the second city of Kharkiv.

"While he may make gains on the battlefield, he will pay a continuing high price over the long run," U.S. President Joe Biden said at his State of the Union address. Straying from the prepared text, Biden added "He has no idea what's coming." He did not elaborate. 

 The invaders' advances have been met with fierce resistance by Ukrainian forces and a miles-long Russian military convoy north of Kyiv has made little progress towards the capital.

In a video address on Wednesday, Zelenskiy said nearly 6,000 Russians had been killed in the first six days of Moscow's invasion, and that the Kremlin would not be able to take his country with bombs and air strikes.

Biden further ratcheted up sanctions on Moscow, joining the European Union and Canada in banning Russian planes from U.S. airspace.

 
He also said the Justice Department would seek to seize the yachts, luxury apartments and private jets of wealthy Russians with ties to Putin.

U.S. lawmakers stood, applauded and roared, many of them waving Ukrainian flags and wearing the country's blue and yellow colours, as Biden delivered his address to the chamber of the House of Representatives. 

Russian forces have taken control of Kherson, a city of nearly a quarter million people just north of Crimea, the peninsula annexed by Russia in 2014, a Russian defence ministry spokesperson said. Strategically located on the Dniepr river, the provincial capital was the biggest city to fall to Russian forces so far.

The southeast city of Mariupol had been under intense shelling since late Tuesday and was unable to evacuate wounded, according to its mayor.

A senior U.S. defense official said on Tuesday the invading force's advance on Kyiv has stalled due to logistics problems, including shortages of food and fuel, and some units appeared to have low morale. 

'STOP BOMBING PEOPLE'

On Tuesday, Ukraine's leader called on Russia to stop bombarding civilians and resume talks.

"It's necessary to at least stop bombing people, just stop the bombing and then sit down at the negotiating table," Zelenskiy told Reuters and CNN in a joint interview in a heavily guarded government compound in Kyiv.

At least 21 people were killed and 112 wounded in shelling in Kharkiv in the last 24 hours, regional governor Oleg Synegubov said on Wednesday. 

More than 450,000 people have fled Ukraine to Poland, and a further 113,000 to Romania. 

The United Nations General Assembly is set to reprimand Russia on Wednesday and demand that Moscow stop fighting and withdraw its military forces. 

Putin ordered the "special military operation" last Thursday in a bid to disarm Ukraine, capture the "neo-Nazis" he says are running the democratic country of 44 million people and crush its hopes of closer ties to the West.

West of Kyiv, in the city of Zhytomyr, four people, including a child, were killed on Tuesday by a Russian cruise missile, a Ukrainian official said. 

In Ukraine's largely Russian-speaking city of Donetsk, in territory controlled by Russian-backed separatists, authorities said three civilians had been killed by Ukrainian shelling.

Reuters was unable to confirm any of the reports of casualties.

Vastly outmatched by Russia's military, in terms of raw numbers and firepower, Ukraine's own air force is still flying and its air defences are still deemed to be viable - a fact that is baffling military experts. 

WEAPONS AND SANCTIONS

Ukraine, which is not a member of NATO, has called on the U.S.-led military alliance to implement a no-fly zone over Ukraine - a request rejected by Washington, which fears stoking a direct conflict between the world's two biggest nuclear powers.

Washington and its allies have instead sent weapons to Kyiv.

Ukrainian Defence Minister Oleksii Reznikov said on Wednesday the country was set to receive Stinger and Javelin missiles from abroad, as well as another shipment of Turkish drones.

Several dozen Japanese men have answered a Ukrainian call for foreign volunteers to fight Russia's invasion, according to a media report on Wednesday. In Taiwan, the president, vice president and prime minister all pledged to donate their salaries to Ukraine relief efforts. 

Isolating Russia diplomatically, the West's main strategy is shutting off Russia's economy from the global financial system, pushing international companies to halt sales, cut ties, and dump tens of billions of dollars' worth of investments.

Exxon Mobil joined other major Western energy companies including British BP PLC and Shell in announcing it would quit oil-rich Russia over the invasion. 

Apple Inc (AAPL.O) stopped sales of iPhones and other products in Russia, and was making changes to its Maps app to protect civilians in Ukraine. Alphabet Inc's (GOOGL.O) Google dropped Russian state publishers from its news, and Ford Motor suspended operations in the country. 

U.S. airplane manufacturer Boeing (BA.N) said it was suspending parts, maintenance and technical support for Russian airlines. 

Russia on Tuesday placed temporary restrictions on foreigners seeking to exit Russia assets, meaning that billions of dollars worth of securities held by foreigners are at risk of being trapped. 

Defying the U.S.-led economic campaign to against Russia, Mexico's leftist President Andres Manuel Lopez Obrador said Mexico will not impose sanctions. 

Reuters