The source said the members were likely to be trained abroad but did not give an estimate of how many there would be.
To keep a degree of order, the government relies on numerous militias made up of thousands of Libyans who took up arms against Gaddafi. The groups provide what passes for official security but also what poses the main threat to it.
The government has taken a twin-track approach, saying it will shut down rogue groups but licensing many of the most powerful armed brigades.
Almost 6,000 former rebel fighters have begun training to be policemen under a drive to disarm militias, the new interior minister said in an interview last week.
"THIS IS NOT SWITZERLAND"
Confirming the government plan for a diplomatic security unit, a foreign ministry source said diplomats currently had to advise Libyan authorities if they planned to travel more than 50 miles from their base.
"Even when the force is established, diplomats need to take care of themselves. This is not Switzerland," the source said.