The UK government said on Thursday it was sending 600 troops to Afghanistan to help British embassy staff leave the country, after the United States announced a similar deployment as the Taliban makes rapid gains.
"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," Defence Secretary Ben Wallace said.
"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 personnel will deploy to Afghanistan on "a short-term basis" due to "the increasing violence and rapidly deteriorating security environment in the country," the Ministry of Defence (MoD) said.
The number of staff working at the British Embassy in Kabul has already been reduced to a small team focused on providing consular and visa services for those needing to rapidly leave the country, it added.
Britain's Foreign Office changed its travel advice last Friday to recommend that all British nationals leave Afghanistan "as soon as possible".
The military deployment will provide "force protection and logistical support" for the relocation of remaining British nationals where required, according to the MoD.
Troops will also help accelerate the UK government's programme relocating Afghans who supported British military personnel operating inside the country over the past two decades.
"This will help to make sure interpreters and other Afghan staff who risked their lives working alongside UK forces in Afghanistan can relocate to the UK as soon as possible," the MoD said.