Sheikh Nasser al-Mohammad al-Sabah's government resigned last year after some opposition lawmakers accused it of having made a series of illegal financial transfers via Kuwait's overseas embassies.
He was questioned last week by a tribunal that has jurisdiction over past and present ministers as part of an ongoing inquiry into alleged graft under the previous administration, , a source with knowledge of the matter said on Sunday., confirming a report in al-Sabah newspaper.
Sheikh Nasser, a nephew of Kuwait's ruler, has denied any wrongdoing. The source declined to be named because of the sensitivity of the investigation. Sheikh Nasser's lawyer was not immediately available for comment.
It is the first time that a complaint against a former prime minister and a member of the ruling al-Sabah family has been investigated at such a high level in the Gulf oil producer. The tribunal will now question members of parliament as witnesses to the alleged events, the newspaper said.
A source in the public prosecutor's office said earlier this year that a court would investigate a complaint against Sheikh Nasser over the allegations.
When the issue first came to light last year protesters and opposition lawmakers staged a series of demonstrations outside parliament that culminated in the storming of the chamber, eventually forcing the government to resign and triggering the dissolution of the assembly.
A snap election in February gave Islamist-led opposition candidates a majority in parliament.
Since then, opposition MPs have quizzed the current prime minister, Sheikh Jaber al-Mubarak al-Sabah, over his handling of the investigation, highlighting continued discord in the region's most outspoken parliament.
He was quizzed again by a parliamentary panel on Saturday, al-Sabah reported.