John Howard, the Australian prime minister, said he knew little about the case other than what details had been revealed in media reports.
"Did we try and get anybody to assassinate the prime minister of the Solomon Islands? Of course not," Howard said.
The Australian department of foreign affairs and trade also denied the government had any involvement, and urged the Solomon Islands' judiciary to fairly examine the allegations.
"It is preposterous to suggest that the Australian government had any involvement in this alleged assassination attempt," a statement from the department said.
"We would expect that these allegations would be rigorously and fairly examined, that innuendo would be dismissed and the facts would be established," it said.
A magistrate ordered Johnson to be held in custody until February 7, when the court in the Solomon Islands' capital, Honiara, will consider his bail application.
He has been charged with conspiracy to commit murder and conspiracy to commit a felony.
Prosecutors allege that Johnson and four other men, who were not named in court, conspired to murder Sogavare.
The men allegedly met at a Honiara hotel and planned the crime between January 18-23.
Johnson was arrested at the hotel on Monday.
His alleged co-conspirators have not been found, prosecutors told the court.
Civil collapse
Johnson's lawyer, Patrick Lavery, told Australian Broadcasting Corporation radio that the allegations were "crazy," and that the prosecution's evidence amounted to nothing more than "drunken conversation".
Australia has led an international military and police force in the Solomon Islands since 2003, when the islands' former government invited the force to bring the nation back from the brink of economic and civil collapse.
But last year, Australia threatened to cut the Solomons' aid, amounting to $168 million for the fiscal year ending June 2007, unless Sogavare's government tackles corruption and improves its performance.