
The Ha'aretz daily quoted members of Israel's Amnesty International branch as confirming that the hunger strike started late Wednesday.
The Israeli Prison Service said that the detainees sent back their meals to the prison guards.
This is not the first time that migrants, mainly from Eritrea and South Sudan, go on hunger strikes to protest against their lockup.
The Israeli law of infiltration, which was amended in January 2012, enables to lock up asylum seekers for up to three years and it does not differentiate between asylum seekers, refugees and illegal migrants.
There are currently 2,000 African migrants locked up in the Saharonim detention facility, including women and children.
In May 2012, former Israeli interior minister Eli Yishai announced the "Going Home" repatriation program.
Yishai considers the Africans as "demographic threat" to the Jewish character of the state and an economic burden on social services.
Since the program's inception, nearly 2,000 South Sudanese asylum-seekers have been expelled, more than a dozen of whom have perished due to dire health and sanitary conditions.