Alma Shalabayeva, the wife of exiled banker Mukhtar Ablyazov, a fierce critic of Kazakhstan President Nursultan Nazarbayev, "is in Almaty and prohibited from leaving the city," prosecutors said in a statement to AFP.
Shalabayeva is "suspected of taking a bribe in a case of false passports," prosecutors said, adding that she had not so far been charged.
Several police and judiciary officials were convicted in June as part of the case.
The expulsion from Italy of Shalabayeva and her six-year-old daughter sparked a huge scandal in Italy, forcing the interior ministry's chief of staff to resign.
On May 29th the Italian police raided Shalabayeva's home near Rome in search of Ablyazov, but didn't find him.
Shalabayeva and her daughter were deported to Kazakhstan on May 31st without being given an opportunity to appeal against the deportation or to seek a political asylum in Italy - contrary to Italian and European laws.
The Italian authorities accused Shalabayeva of holding a fake passport, and had them put on a plane to Kazakhstan two days later.
Three UN experts on Thursday asked the Italian authorities to facilitate their return to the country.
Alma Shalabayeva and her six-year-old daughter were legal EU residents, the experts said, charging that Italian authorities had violated guarantees of due process of their right to appeal against deportation and to apply for asylum.
Mukhtar Ablyazov was jailed in 2002 and subsequently went into opposition to the strongman President Nazarbayev's regime.
After he was released, he led the BTA Bank that saw rapid development, but later fled the country fearing persecution. He initially took refuge in London but is now believed to have left, fearing for his security. His current whereabouts is unclear.
Ablyazov is believed to be an important financial backer of the sidelined anti-Nazarbayev opposition. Kazakhstan has also accused him of being behind a series of violent attacks in the country.