The authorities began an operation on Monday aimed at mustering a thousand men, "who won't go directly to the front, but will be used to secure important sites", one source said.
Colonel Abdoulaye Mounkaila, a retired officer and member of Niger's Military Reserve Commission, told state TV that the defence ministry was "appealing to former soldiers and gendarmes who have been retired five years" or less.
The returnees -- for which specialists are particularly sought -- will provide "relief for the defense and security forces, which are constantly on active duty", he said.
Niger is suffering from the spillover from the ongoing jihadist insurgency in northeast Nigeria, which has affected neighboring states in the Lake Chad region.
Militants who swept in from neighboring Mali have been carrying out bloody attacks in the southwest of the country since 2015.
In 2020, the country had declared the goal of doubling armed forces personnel, from 25,000 to 50,000 over the following five years.
It has also pushed back retirement age for non-commissioned ranks from 47 to 52.
The country is getting logistical and training support from former colonial power France, as well as from the United States, Italy, Germany and Belgium.
France and the United States both have important military bases in the vast arid country, while Germany has a logistics base.