Ukrainian President Volodymyr Zelensky has arrived in the UK for his first visit since the Russian invasion of his country.
On his surprise trip, Mr Zelensky is due to meet Prime Minister Rishi Sunak and deliver an address to Parliament, a rare occurrence for a foreign leader.
The visit is only Mr Zelensky's second outside Ukraine since the war began after he made a whirlwind trip to the United States in December.
The Ukrainian leader will also visit troops being trained in the south west of England later today.
Buckingham Palace also confirmed that Mr Zelensky will have an audience with King Charles.
Mr Sunak announced plans to train Ukrainian pilots which would pave the way for them to be able to fly Nato-standard jets - a key request from Ukraine.
The Prime Minister said: “President Zelensky’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.
"Since 2014, the UK has provided vital training to Ukrainian forces, allowing them to defend their country, protect their sovereignty and fight for their territory.
"I am proud that today we will expand that training from soldiers to marines and fighter jet pilots, ensuring Ukraine has a military able to defend its interests well into the future.
"It also underlines our commitment to not just provide military equipment for the short term, but a long-term pledge to stand shoulder-to-shoulder with Ukraine for years to come."
The UK is also set to announce new sanctions targeting those who have helped Vladimir Putin get rich and firms which have profited from the war.
The expansion of the UK's training programme to include jet fighter pilots is significant as Mr Zelensky has been urging Western nations to supply planes.
The UK has so far refused, arguing that the RAF's F-35 and Typhoon jets take too long for pilots to train on.
But the announcement by No 10 signals a shift for the future, and officials said that "as part of that long-term capability investment" the UK will work with Ukraine and international allies "to co-ordinate collective support to meet Ukraine's defensive needs".
Ukrainian troops are already being trained in the use of Challenger 2 tanks, which are expected to be sent to the country next month.
Mr Sunak will offer longer-range firepower to help counter Russia's ability to strike at Ukraine's towns and energy facilities.
Commons Speaker Sir Lindsay Hoyle said: "It is an honour to host President Zelensky of Ukraine in Westminster Hall later today.
"The President will address Members of both Houses about the ongoing situation in his country."
