About 600 British personnel are to deploy to Afghanistan on a short-term basis, helping UK nationals leave the country.
Defence Secretary Ben Wallace made the announcement in light of the recent Taliban resurgence.
British nationals will be supported alongside former Afghan staff who are seeking sanctuary in the UK.
Meanwhile, the number of staff working at the British Embassy in Kabul has been reduced to a core team – focused on consular and visa services for those needing to leave an increasingly insecure Afghanistan.
Defence Secretary Ben Wallace said: "I have authorised the deployment of additional military personnel to support the diplomatic presence in Kabul, assist British nationals to leave the country and support the relocation of former Afghan staff who risked their lives serving alongside us.
"The security of British nationals, British military personnel and former Afghan staff is our first priority.
"We must do everything we can to ensure their safety," he added.
The military support will arrive in Kabul in the coming days.
Cover image: Mountains near Kabul (Picture: US Department of Defense).