South African prosecutors are asking the nation's highest court to reject a bid by Oscar Pistorius' lawyers to appeal the double-amputee runner's murder conviction.

Luvuyo Mfaku, spokesman for the National Prosecuting Authority, said Monday that prosecutors have filed papers with the Constitutional Court arguing that Pistorius' appeal is not valid.

Lawyers for Pistorius, who killed girlfriend Reeva Steenkamp in his home in 2013, had appealed to South Africa's highest court, saying another court erred when it overturned a manslaughter conviction and declared the Olympic athlete guilty of murder.

Pistorius is under house arrest while the Constitutional Court decides if it will hear the case. Sentencing on the murder conviction is scheduled for April 18.