Fiji saw its most recent coup less than a year ago
Businessmen, politicians and former soldiers were among those detained, and will be charged, police say, on Monday.
New Zealand Prime Minister Helen Clark said one of those arrested, a New Zealander, had been badly beaten.
Mr Bainimarama came to power after a bloodless coup in December 2006, but has promised elections in early 2009.
He has pledged to abide by the results.
Fiji has seen four coups in the past two decades.
Military help
No concrete details have been given about the alleged plot, but Fiji Police Commissioner Esala Teleni said "several suspects and others are believed to be armed".
He said more arrests were possible, adding that the police has requested the assistance of the military.
He added that cabinet ministers and military officers were also being targeted by the plotters.
A New Zealand businessman, Ballu Khan, who is based in the Fijian capital, Suva, was among those arrested.
He was allegedly so badly beaten that he was unable to talk, and a hospital source quoted by Reuters news agency said he had a broken jaw and ribs.
New Zealand diplomats had difficulty in obtaining access to Mr Khan.
"They held this man back from proper health care in a hospital for far too long and they beat him when he was in custody. That is disgraceful," said the New Zealand prime minister.
Six men were charged Monday with the attempted assassination of Commodore Frank Bainimarama, the commanding officer of the Republic of Fiji Military Forces and the interim Prime Minister of Fiji since January 5, 2007.

Police Commissioner Commodore Esala Teleni said Monday that sixteen people were being detained in connection to a plot to assassinate the Bainimarama and several Cabinet Ministers.

Bainimarama said, in a statement Monday, "There are obviously disgruntled groups out there who are feeling the full impact of the interim government's 'Clean Up Campaign', such people have the potential to go to extremes in undermining the work which the interim government has been mandated to undertake". 

The men are charged with treason, inciting mutiny and conspiracy to murder. They appeared in a Suva court Tuesday. The case was adjourned for bail hearing Wednesday morning after the prosecutor requested time to amend the charges. 

A New Zealand businessman, Ballu Khanwas among the men arrested. Teleni states he had "minor injuries" as a result of resisting arrest. Others have reported that he was hospitalized for a broken jaw and ribs as a result of a police beating.  New Zealand's Prime Minister Helen Clark said the way Khanwas has been dealt with is "disgraceful".

Fiji news media initially reported that police suspected the plot could be linked to foreign aid groups and neighboring countries.

Clark denied that allegations stating that "of course the New Zealand government hasn't been involved in any such thing," 

Australian Foreign Minister Alexander Downer called the allegation absurd, stating "It is completely false to suggest that the Australian government would consider assassinating Commodore Bainimarama and coup leaders in Fiji or that we would in any way wish to see any death occur in Fiji".

Bainimarama later told journalists at a press conference that the police never suspected foreign involvement and the “report was distorted and sensationalized”.

Frank Bainimarama became prime minister in a bloodless 2006 coup, replacing the democratically elected government of Prime Minister Laisenia Qarase. Bainimarama accused the Qarase government of corruption and being too soft on those involved in the 2000 coup.