WASHINGTON (Reuters) - British Prime Minister Keir Starmer will tell NATO leaders on Thursday they must send a clear message to Russian President Vladimir Putin of unity in their support for Ukraine, and he re-committed to delivering a 3 billion pound military aid package for Kyiv.

At his first international meeting after winning a landslide election victory, Starmer enjoyed a warm welcome from NATO leaders, some of whom can only envy his large majority at home and the stability it should deliver for his new administration.

Days into his leadership, Starmer recommitted to the former Conservative government's pledge to deliver 3 billion pounds ($3.9 billion) a year of military support to Ukraine until 2030-31 and beyond if needed, underlining continuity in Britain's role as being one of Kyiv's most active and vocal backers.

"NATO was founded by the generation who defeated fascism. They understood not just the value of our strength, but the strength of our values," he will say, according to excerpts of his speech.

"Those values are under attack once again. Putin needs to hear a clear message ringing out from this summit - a message of unity and determination, that we will support Ukraine with whatever it takes, for as long as it takes to uphold our shared values and our shared security."

Hours after Starmer's Labour Party won an election to sweep the Conservatives from power, he deployed his newly appointed ministers to show Britain's continued support for Ukraine.

His foreign minister, David Lammy, toured Germany, Poland and Sweden over the weekend to emphasise their shared backing for Ukraine, and Defence Secretary John Healey headed to Kyiv to tell President Volodymyr Zelenskiy the Labour government would have an "ironclad" commitment to supporting Ukraine.

Healey said the new government would speed up the military aid promised by its predecessor in April and pledged new deliveries of ammunition, missiles, boats and artillery.

Starmer's arrival at NATO is an early opportunity to establish his direction of travel, promising to replace what he calls the chaos of the Conservative years with stability.

On Tuesday, he said his government wanted to increase Britain's defence spending to reach 2.5% of GDP, but was again cautious in setting out any timetable, underlining the increase could not come at the expense of fiscal prudence.

He said he would launch a defence review next week, which would look at a possible roadmap to achieving that goal but also at "the challenges that we face, the capabilities and making sure that the two match".

He told reporters on the plane to Washington that defence and security was the first priority of government.

"And that is why we are carrying out the strategic review. That is wider than the money question," he said.

His armed forces minister Luke Pollard told Sky News on Wednesday the review would be completed within the next year.

($1 = 0.7794 pounds)

(Reporting by Elizabeth Piper; Editing by Angus MacSwan)

By Elizabeth Piper