The FBI has managed to unlock the iPhone of the San Bernardino gunman without Apple's help, ending a court case, the US justice department says.

Apple had been resisting a court order issued last month requiring the firm to write new software to allow officials to access Syed Rizwan Farook's phone.

But officials on Monday said that it had been accessed independently and asked for the order to be withdrawn.

Farook and his wife killed 14 in San Bernardino, California, in December.

They were later shot dead by police.

The FBI said it needed access to the phone's data to determine if the attackers worked with others, were targeting others and were supported by others.

US officials said Farook's wife, Tashfeen Malik, had pledged allegiance to the so-called Islamic State on social media on the day of the shooting.