Serbian police have detained former Yugoslav army chief of staff Nebojsa Pavkovic.
Pavkovic was identified with army tactics in Kosovo
Radio reports said the move was in connection with the clampdown on organised crime which has followed the murder of the Serbian Prime Minister, Zoran Djindjic, last month.
General Pavkovic is not a suspect in the killing, reports say. The Reuters news agency said he was being held over the apparent authorisation of a military helicopter for an alleged crime committed under former Yugoslav President Slobodan Milosevic.
The reports came as US Secretary of State Colin Powell prepared to visit Belgrade later on Wednesday to show US support for continued reform and to encourage co-operation with the Hague war crimes tribunal.
The American State Department said the visit would underscore US commitments to Serbia and Montenegro's fight against organised crime, and to the region's long-term stability and economic growth.
Ivan Markovic, a leading member of the party led by Mr Milosevic's wife, Mira Markovic, was also detained for a second time.
The arrests came as police said they were closing in on the suspected organised crime leader and organiser of Mr Djindjic's assassination, Milorad Lukovic, after finding passports in his name.
Police say they are getting close to suspected ringleader Milorad Lukovic
Police have detained more than 3,000 people since the 12 March killing, and are seeking an international warrant for the arrest of Mrs Markovic.
They are also seeking to question her over the killing of former Serbian president Ivan Stambolic, whose remains were found last week.
Mrs Markovic, who is currently in Moscow, has denied any involvement in the deaths.
General Pavkovic, an ally of Mr Milosevic, was closely identified with the army's repressive tactics in the province of Kosovo in the late 1990s.
He later switched support to the new democratic authorities, after refusing to use troops against demonstrators taking part in protests that led to the overthrow of Mr Milosevic.
He was backed by Mr Milosevic's successor Vojislav Kostunica, despite western pressure for his removal and investigations of alleged war crimes in Kosovo.
But Mr Kostunica removed him in March last year following a spy scandal which led to the arrest of a deputy prime minister and a US diplomat.
General Pavkovic had tried to distance himself from the intelligence operation which led to the arrests.