JOHANNESBURG (Reuters) - South Africas Supreme Court increased Oscar Pistorius murder sentence on Friday to 13 years and five months after the state argued that his original sentence of six years was shockingly lenient.

Pistorius was imprisoned in July last year after being found guilty on appeal of murdering girlfriend Reeva Steenkamp on Valentines Day 2013 in a case that attracted worldwide interest.

The athlete was not in court for Fridays ruling where the court handed down the minimum 15-year sentence prescribed for murder in South Africa, and subtracted the years Pistorius had already served.

The sentence imposed... in respect of murder is set aside and substituted with the following: the respondent is sentenced to imprisonment for a period of 13 years and five months, the judge said, reading out the courts decision.

The athlete was originally convicted of manslaughter and sentenced to five years in jail. That conviction was increased to murder by the Supreme Court in December 2015 and his sentence was increased to six years by trial judge Thokozile Masipa.

There was no immediate comment from the Pistorius or Steenkamp families.

Rights groups in a country beset by high levels of violent crime against women say Pistorius received preferential treatment compared to non-whites and those without his wealth or international celebrity status.