Sir Keir Starmer has arrived in Kyiv to sign what Downing Street is calling a "landmark 100-year partnership" with Ukraine.

The pact would formalise economic and military support already pledged to the country, and offers more.

It is the prime minister's first visit to the country since taking office last summer, in a show of support for Ukraine days before Donald Trump re-enters the White House.

Ukrainian President Volodymyr Zelensky is keen to discuss firm security guarantees from key allies such as the UK, wary that a new US administration could start pushing Ukraine to make peace with Russia.

Unlike other prime ministers who have rushed to Kyiv, Sir Keir has taken his time to visit, but after six months in office he has come to Ukraine pledging long-term support against what he calls Russia's "illegal and barbaric invasion".

He was greeted at Kyiv railway station by the UK's ambassador to Ukraine, Martin Harris, and the Ukrainian envoy to London, Valerii Zaluzhnyi.

The highlight of the visit would be the signing of the 100-year partnership agreement, Zuluzhnyi said, which would cover areas from science to culture, with a particular focus on security.

Speaking as he travelled to the country, Sir Keir said: "This is not just about the here and now, it is also about an investment in our two countries for the next century."

"[Russian President Vladimir] Putin's ambition to wrench Ukraine away from its closest partners has been a monumental strategic failure. Instead, we are closer than ever, and this partnership will take that friendship to the next level," he added.

Trump's choice to become secretary of state, Marco Rubio, said earlier this week that both countries would have to make concessions to see an end to the war.

Thursday's announcement includes more military and economic aid to prove that, as well as increased military collaboration on maritime security and drone technology, and healthcare.

Zelensky has previously said he is looking towards the UK for help getting security guarantees to deter future attacks.

Joining Nato is towards the top of his wish list, but Ukraine also wants its allies to send peacekeepers to the country if fighting does stop, to patrol the current frontline which could become a buffer zone in any peace agreement.

Ahead of the visit, Zelensky said this was something he would discuss with the prime minister.

It builds on £12.8bn of support the UK has already given to Ukraine. The country has also already committed to giving the country £3bn in military aid every year for "as long as it takes".

Ukraine has already been using British-supplied Storm Shadow missiles to attack Russian military facilities far from the border.

Their arrival late last year was welcomed by Kyiv, and slammed by Moscow.

The partnership, formed of a treaty and a political declaration, is due to be presented to Parliament in the coming weeks.

Plans for it had begun under the previous Conservative government.

Sir Keir previously visited Ukraine when he was leader of the opposition in 2023, and has hosted President Zelensky twice at Downing Street since entering office.

Additional reporting by Alex Smith.