The 114 people who contracted COVID-19 are in isolation, according to the notice, which was approved by U.S. Ambassador Ross Wilson.
"Military hospital ICU resources are at full capacity, forcing our health units to create temporary, on-compound COVID-19 wards to care for oxygen-dependent patients," the notice said. "95% of our cases are individuals who are unvaccinated or not fully vaccinated."
Across the country, infection rates have surged by around 2,400% in the past month, according to the International Federation of Red Cross and Red Crescent Societies statement Thursday.
The notice said anyone coming to the embassy should be vaccinated prior to arrival, adding that "failure to do this puts everyone in the community at risk."
The outbreak comes amid the U.S. military withdrawal from Afghanistan, which is more than 50% complete, according to a U.S. Central Command update earlier this week.
"We must break the chain of transmission to protect one another and ensure the Mission's ability to carry out the nation's business," Thursday's notice said.
The U.S. Embassy in Afghanistan announced last week that it was suspending visa operations due to the surge in COVID-19 cases across the country.
Still, applications will continue to be processed at the chief-of-mission stage in Washington, U.S. Department of State Principal Deputy Spokesperson Jalina Porter said last Friday.
In response to the suspension of visa operations, Rep. Michael McCaul, R-Texas, who serves as the lead Republican on the House Foreign Affairs Committee, said in a statement President Joe Biden "should explore the option of humanitarian parole."