Law enforcers armed with a warrant cordoned off and searched the apartment of Yury Lutsenko, a key figure in Ukraine's 2004/5 pro- democracy Orange Revolution, and currently one of the harshest critics of the country's pro-Russia government.
Local media was on the scene but neither Lutsenko nor police commented on the search.
Ukraine's Prosecutor General Oleksander Medved'ko, told the Interfax news agency the search stemmed from an investigation by his office into allegations that Lutsenko had handed out fire arms without license to political friends, while serving as interior minister.
Lutsenko held the post, which also made him the head of the national police force, from March 2005 to December 2006, when a pro- Russia parliament majority ousted him from office.
Reduction of corruption among police and government officials had been the interior ministry's top priority while Lutsenko held the job.
Handgun ownership is illegal in Ukraine, with the exception of some law enforcement personnel.
Lutsenko, in past statements, had claimed the allegations against him and the investigation was a political vendetta by the country's pro-Russia government, which resented his efforts to reduce corruption.
"We have a warrant and we are following up the results of a legitimate investigation," Medved'ko said. "There are no political motivations in this case."
Vasyl Kisilev, a top member of the parliament majority and a frequent target of Lutsenko's charges of corrupt ties between government and big business, went even further, describing Lutsenko as "a nobody. His name means nothing."
Ukraine Prime Minister Viktor Yanukovich, as taken an overtly neutral stance on the matter, saying he would not interfere with a criminal investigation and that he had not asked for details of the case against Lutsenko.
The search of Lutsenko's apartment marks the most obvious instance yet of Ukraine's current government attempting to settle accounts with the opposition, which held power from March to September 2006.
Yanukovich at the time said he was a frequent victim of political repression. In remarks to reporters on Tuesday, he denied his government was pursuing political vendettas.