Sir Keir Starmer is reportedly considering increasing defence spending to meet a target early - at a potential cost of billions of pounds.
The BBC reports the prime minister hinted at the possibility during a security conference in Germany over the weekend, at which he told other world leaders: "To meet the wider threat, it's clear that we are going to have to spend more, faster."
Last year, Starmer vowed to spend 2.5% of the UK's GDP on core defence by April of 2027.
He also set out an "ambition" to raise defence spending to 3% of GDP in the next parliament.
The BBC has learned the prime minister's aides are now looking at proposals to meet that 3% ambition by the end of the current parliament, which could last until 2029.
No formal decision has yet been made and the BBC reports the Treasury is cautious.
Last month it was reported the Ministry of Defence (MOD) needed an extra £28billion to meet existing costs over the next four years.
Sir Richard Knighton, chief of the defence staff, told MPs in January: "We cannot do everything we would want to do, as quickly as we want to do it, within the context of the budget we have set."
FSTE100
The UK's flagship share index, the FTSE 100, was up 29 points at 10,465 shortly after opening this morning.
Brent crude oil futures were down 0.19% at $67.55 a barrel.
Companies reporting today
BHP Group* - Half Year Results