President Volodymyr Zelenskiy was due in London on Wednesday for only his second trip abroad since Russia invaded Ukraine and he won promises of new military aid, including training on advanced Nato fighter jets the West has so far held back from supplying.

British Prime Minister Rishi Sunak's office said Zelenskiy would address Parliament and visit Ukrainian troops training in Britain.

"President Zelenskiy's visit to the UK is a testament to his country's courage, determination and fight, and a testament to the unbreakable friendship between our two countries," Sunak said in a statement.

Sunak's office announced additional sanctions on Russia, as well as plans to accelerate the supply of military equipment to Kyiv. For the first time, Ukraine's air force and marines would now be included in the British training programme.

"The training will ensure pilots are able to fly sophisticated Nato-standard fighter jets in the future," it said, although it gave no timeframe.

That appeared to signal a notable shift in Western support, as countries have so far held back from providing jets or weapons that could strike deep into Russia.

Zelenskiy is also seen as likely to attend an EU summit later this week as he drums up support from Western allies at the outset of what Kyiv says will be a decisive second year of the war. The bloc's leaders are gathering in Brussels on Thursday and Friday, and Zelenskiy has a standing invitation, although official plans have not been announced.

Zelenskiy visited the United States in December and addressed the US Congress on his only known trip abroad since Russia launched its full-scale invasion in February last year.

Western countries have dramatically scaled up their pledges of military support for Ukraine since the start of the new year, including promises of hundreds of tanks and armoured vehicles. Kyiv still wants longer-range missiles and warplanes.

After major Ukrainian gains in the second half of 2022, Russia has recovered momentum, with tens of thousands of freshly mobilised troops reaching the front.

Relentless battles by Russian forces

Russian forces have made incremental progress in relentless winter battles in the east of the country in recent weeks, which both sides describe as some of the bloodiest fightings of the war.

Kyiv says it expects Moscow to broaden that offensive with a big push as the Feb 24 first anniversary of the invasion approaches.

"They need to have something to show before their people and have a major desire to do something big, as they see it, by this date," Ukraine's national security chief Oleksiy Danilov told Reuters on Tuesday in an interview.

He predicted Russia, which has focused lately on the Donetsk region in the east, would try new attacks on Kharkiv further north or Zaporizhzhia further south.

"How successful they'll be will depend on us."

Russia launched its "special military operation" to combat what it describes as a security threat from Ukraine's ties to the West, and says Western supplies of weapons to Kyiv will only prolong the war. It claims to have annexed four Ukrainian provinces last year.

Ukraine says the only way to stop the war is for the West to give it the capability to drive Russian forces out.

Western fighter jets are at the top of Ukraine's wishlist for weapons. Neither Moscow nor Kyiv enjoys air superiority over Ukraine, which has limited the use of piloted aircraft on both sides in the war.

The United States and Britain have suggested they would not send their own fighter jets to Ukraine. But other countries have indicated that they might do so, keeping the door open for a collective decision by Western allies.

- Reuters