A supplier enlisted to make sapphire screens for Apple mobile devices on Friday urged a bankruptcy court to free it from contracts it branded "oppressive and burdensome."

Sapphire touch screens are a very tough synthetic replacement for the glass currently used on many Apple mobile devices, and are already used in a limited way for particularly sensitive parts of devices.

The synthetic screens were also expected to be used in the Apple Watch and in some versions of the latest iPhones.

US-based GT Advanced Technologies (GTAT) "believes that it has many claims against Apple arising out of its business relationship," lawyers for the firm said in paperwork filed in US Bankruptcy Court.

"The agreements imposed oppressive and burdensome terms and obligations on GTAT."

GTAT also asked the court to let it wind down synthetic sapphire manufacturing facilities in two states to extinguish an "ongoing cash burn" that threatens to devour its liquidity.

GTAT argued in court documents that contracts benefiting Apple shifted the company's business model from primarily supplying sapphire-making equipment to being a sapphire materials manufacturer.

GTAT has formally filed for petitioned for bankruptcy protection, bringing into question where Apple would turn for its supply of sapphire touch-screens.

GTAT told the court that careful evaluation had led it to conclude that to protect its assets it needs to wind down sapphire facilities in Arizona and Massachusetts and eliminate supporting staff at its offices in New Hampshire.

Ending sapphire making operations was expected to mean the loss of 890 jobs, according to the legal motion.

Apple did not respond to an AFP request for comment but has been quoted in press reports as saying it was "surprised" by GTAT's decision to file for bankruptcy.

The GTAT group makes and supplies equipment and materials for the electronics, solar and LED light industries.