The Defence Secretary says the number of British troops in Afghanistan could be reduced if the United States goes ahead with its own reductions in the country.
Acting US Defense Secretary Christopher Miller announced on Wednesday that the number of troops in Afghanistan will fall from around 4,500 to 2,500 and from 3,000 to 2,500 in Iraq, with the withdrawals effective by January 2021.
Speaking to Sky News on Thursday, Ben Wallace said: "We’ll see the details.
"The United States have only just announced the exact number that they are going to reduce to but I suspect if they are reducing, at some stage, we will come down."
He added the UK does not "have a massive force" in comparison to the US, but they will do what needed to "keep people safe and ensure that we do our best to ensure that Afghans are kept protected as well".
The announcement by the Americans follows commitments made to reduce troop numbers in the region in recent months.
President Donald Trump said last month that remaining US personnel in Afghanistan should be "home by Christmas" following the previous withdrawal of thousands of troops, while pledges have also been made to remove servicemen and women from Iraq.
Mr Miller said he had spoken to Afghan and Iraqi officials, as well as NATO Secretary General Jens Stoltenberg.
Mr Stoltenberg warned earlier in the week that the alliance could pay a heavy price for withdrawing troops from Afghanistan "too soon".
There are about 1,000 British troops currently based in Afghanistan as part of Operation Toral – their contribution to the NATO Resolute Support mission.
The UK ended its combat role in Afghanistan in 2014 but personnel remain deployed to the country in non-combat roles, including providing security to NATO advisors and government officials, being on standby for emergencies, and training members of the Afghan Security Forces.
In Iraq, meanwhile, 400 UK military personnel have been stationed across several sites.
As part of Operation Shader, British troops have trained more than 100,000 Iraqi and Kurdish Peshmerga forces in weapons maintenance, counter IED, medical and engineering skills.
Commenting on the US announcement, Major General (Retired) Andy Salmon, who was a British Commander in Basra, told Forces News: "The risk in Afghanistan is, if the situation worsens and you decided to withdraw, then there is more of a non-permissive withdraw, which gets more complicated."
He added it is important to "carefully consider" the consequences of "unilateral decisions" in places like Afghanistan and Iraq.
"If you want to exert influence in these places that you've intervened in a mass way, then you've got to have some skin in the game and so, you've got to carefully consider the consequences of any unilateral decision that impact, you know, those dynamics," he said.
Cover image: A library picture of a mountain in Afghanistan (Picture: US Army).