A grieving father has written to Apple head Tim Cook to beg him to unlock his dead son's iPhone so he can retrieve photographs stored on it.

Leonardo Fabbretti, from Italy, wants to unlock the iPhone 6 to access photographs taken by his 13-year-old son Dama who died of bone cancer in September.

The architect said that if the tech giant doesn't help, he would turn to the Israeli mobile forensics firm that reportedly helped the FBI unlock the phone used by gunman Syed Farook in San Bernardino attack.

"Don't deny me the memories of my son," Mr Fabbretti wrote in a letter to Mr Cook on March 21.

Mr Fabbretti told AFP he had given his son, who he adopted from Ethiopia in 2007, an iPhone nine months before his death which he used all the time.

"He wanted me to have access, he added my fingerprint ID," he said. "Unfortunately it doesn't work if the phone is turned off and on again."

Mr Fabbretti said that Cellebrite, which claimed it can crack Apple devices, had offered to open the phone free of charge.

He said that the company should make a charitable donation to Ethiopia or set up a grant for researchers looking into privacy issues if they refuse to help unlock the device.