Prosecutors on Thursday defended their decision to drop four drug-related charges against Shoko Asahara, saying the move is necessary to speed the Aum Shinrikyo founder's trial.

The defense called the decision arbitrary and an abuse of the prosecution's rights, but prosecutors argued that the move, of which the Tokyo District Court was notified Wednesday, "could not be helped."

Asahara's lawyers said the prosecutors' original plan to press 17 charges was intended to overwhelm the defense counsel and prevent a full defense of Asahara, taking advantage of public calls for the trial's immediate conclusion.

The dropped charges included the illegal production of drugs, of which 14 of Asahara's followers have already been found guilty.

The prosecutors said it was natural to make every effort to accelerate the trial and called on the defense to make increased efforts toward that end.

Meanwhile, a former senior Aum member testified during Thursday's hearing that he was ordered to visit Russia to learn how to manufacture "a weapon bigger than pistols" in 1993.

Kenichi Hirose, a former Aum scientist, who was sentenced in July to hang for releasing sarin in the deadly 1995 subway attack and for manufacturing a prototype assault rifle based on the Russian Army's AK-74, said that he believes Asahara thought manufacturing weapons was essential to create an "Aum kingdom."

Upon Asahara's order, he and three other cultists brought parts and other information on the Russian machinegun and gunpowder to Japan to create rifles, he said.

The cult allegedly planned to assemble 1,000 machineguns in 1994 and 1995.