Britain's Prime Minister Theresa May speaks at a general election campaign event at marketing services group Linney, in Mansfield on May 10, 2017. REUTERS/Oli Scarff/Pool

LONDON (Reuters) - British Prime Minister Theresa May promised to increase the country’s defence budget by at least 0.5 percent in real terms every year until 2023 if she wins a June 8 election, adding an extra two years to her party’s existing spending pledge.

May, whose Conservative Party is expected to win the election next month, said the promise was about keeping the country safe and fulfilling Britain’s “obligations to the world”.

“If elected on June 8 I will ensure that the UK continues to spend at least 2 percent of GDP on defence and that the budget rises every year,” May said in a statement.

Alongside the United States, Britain is one of only five countries in the NATO military alliance which meet an obligation to spend 2 percent of economic output on defence -- something May has used to curry favour with U.S. President Donald Trump.

Both Trump and May have repeatedly called on NATO allies to meet the spending target.

In July 2015, then-finance minister George Osborne first announced that Britain would increase defence spending at an above-inflation rate every year until 2021. May’s commitment now runs until 2023.