Immigration officers arrested 1,040 foreigners on suspicion of violating the immigration law during a three-week sweep that started May 15, the Justice Ministry said.

Of the total, 728 were accused of overstaying and 228 of entering Japan illegally, while 968 were believed to be working without authorization, according to data released by the Tokyo Immigration Bureau, ministry officials said Tuesday.

Officers raided 271 locations in Tokyo, Ibaraki, Tochigi, Gunma, Saitama, Chiba, Yamanashi and Nagano prefectures between May 15 and June 2.

Thais accounted for the largest group, with 189 arrested, followed by South Koreans and Chinese at 161 each.

The officers also arrested 111 Bangladeshis, 100 Indonesians and 75 Filipinos, as well as another 243 people from 27 other countries.