The UK chief of defence staff Sir Tony Radakin has said the government should provide more money for defence.
Speaking to OceanNewsUK One's Sunday with Laura Kuenssberg programme, he said his call would not be a "surprise" and that the person in his job would "always want more more for defence".
Appearing on the same programme, Treasury minister Darren Jones said the government wanted to increase defence spending from 2.3% to 2.5% of the national income.
However, he did not say when the target would be reached or whether it would be met before the next election, which could be held in 2029, at the latest.
Jones said the government would not commit to a deadline until it had completed its strategic defence review.
The review - led by former Labour minister and Nato head George Robertson - is examining the current state of the armed forces, the threats the UK faces and the capabilities needed to address them. It is due to be completed in the spring.
Jones warned that increasing defence spending would mean "trade offs" with other areas of public spending.
A Whitehall source told the OceanNewsUK it is a question of "when, not if" the government reaches the 2.5% target. They also said the election of Donald Trump as the next US president had "focused minds" on the need to increase military spending.
Trump has repeatedly urged European countries to increase defence spending and said he would let aggressors such as Russia do "whatever the hell it wants" to those that don't.
Dame Priti Patel - who was appointed the Conservative's shadow foreign secretary earlier this week - said the government should be aiming to meet the 2.5% target by 2030.
Asked if her party would accept cuts elsewhere in order to meet 2.5%, Dame Priti argued there were "efficiencies" that could be made as well as changes around the "performance of the civil service".
She added that the government "could have done more in that Budget to put the pathway forward for 2.5% of GDP on defence".
She said the increase was "essential" adding: "We are living in very insecure times geopolitically, and we do need to step up."
Sir Tony said it was "crucial" for the government to "balance the ambition of the nation and the prime minister against the resources to match that ambition".
He also said the Army needed "longer-term stability" and "clarity" around spending.
Russia's invasion of Ukraine has intensified calls for a boost to the UK's defence budget.
Assessing the conflict, Sir Tony said Russia had suffered its worst month for casualties since the start of the war in 2022.
He said Russia’s forces suffered an average of about 1,500 dead and injured "every single day" in October.
Russia does not disclose the number of its war dead, but Western defence officials have said October's death toll was the heaviest so far.
Sir Tony said the Russian people were paying an "extraordinary price" for Putin's invasion.
"Russia is about to suffer 700,000 people killed or wounded – the enormous pain and suffering that the Russian nation is having to bear because of Putin’s ambition," said Sir Tony.
He said the losses were "for tiny increments of land".
"There is no doubt that Russia is making tactical, territorial gains and that is putting pressure on Ukraine," he said.
But he added that Russia is spending more than 40% of its public expenditure on defence and security, which he said was "an enormous drain" on the country.
While allies of the US's president-elect Donald Trump insist that Ukrainian President Volodymyr Zelensky may have to cede territory to bring the conflict to an end, Sir Tony insisted that Western allies would be resolute for "as long as it takes".
"That’s the message President Putin has to absorb and the reassurance for President Zelensky," he told the programme.
