Jose Padilla, center, is escorted by federal marshalls on his arrival in Miami (File)

A U.S. federal judge in Miami, in the southern U.S. state of Florida, has rejected a motion to dismiss terrorism charges against alleged al-Qaida operative Jose Padilla.

U.S. District Court Judge Marcia Cooke issued the ruling late Monday, rejecting a defense motion for dismissal of the case due to claims of "outrageous government conduct" while Padilla was in U.S. military custody.

Lawyers for Padilla say he was tortured and subjected to harsh treatment for three-and-a-half years while in custody. They say the abuse included constant isolation, shackling in "stress positions" and prolonged sleep deprivation.

Judge Cooke said the torture allegations have no bearing on his case.

Prosecutors have accused the 36-year-old American of conspiring with Islamic extremists around the world in terror plots. His trial is due to begin on Monday.

Padilla was arrested in Chicago in May 2002 upon his return from Egypt and Pakistan. President Bush declared him an "enemy combatant" and ordered him held in military custody. U.S. officials initially accused him of plotting to set off a radioactive "dirty" bomb in the United States, but the current charges against him make no mention of a bomb plot.

Last month, an official from the Navy detention facility testified that Padilla was at times deprived of light, a clock and a Koran, and was forced to sleep on a metal bed frame without a mattress. Padilla had asserted that he was injected with LSD or a truth serum, but the official said it may have been a flu shot.

Padilla's lawyers argue that their client suffers from post-traumatic stress disorder from his detention, and that he is unable to remember details, discuss his interrogations or assist his counsel.

Some information for this report was provided by AP and Reuters.