A senior official says Israel will start rounding up thousands of unauthorized Sudanese migrants and put them in a detention center if they don't leave the country voluntarily.

Interior Minister Eli Yishai says the detentions will begin in mid-October.

Yishai told Army Radio on Thursday that once migrants can't work, "they will get sick of being here and will want to leave voluntarily."

Israel is grappling with an unanticipated influx of 60,000 migrants from Africa, including 15,000 from Sudan. The government insists most came to find better lives, not asylum.

Most are from Sudan and Eritrea, states with repressive regimes.

Israel cannot expel them to their homelands because it has signed an international refugee treaty that bars it from forcibly returning migrants to countries considered liable to persecute them.