Oscar Pistorius is appealing against his recently lengthened prison sentence for the murder of girlfriend Reeva Steenkamp, according to South African media.

Broadcaster EWN said the Olympian filed an application to the Constitutional Court on Tuesday.

The Supreme Court of Appeal last month more than doubled Pistorius's sentence to 13 years, calling the initial six-year sentence "shockingly lenient".

Now the earliest the double-amputee runner will be eligible for parole is 2023.

Pistorius killed Ms Steenkamp in the pre-dawn hours of Valentine's Day 2013, shooting four times through a closed toilet cubicle door with a 9mm pistol.

He claimed he mistook the 29-year-old model and reality TV star for an intruder.

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