Danish submarine inventor Peter Madsen is appealing against his life sentence for murdering Swedish journalist Kim Wall.

Madsen, 47, was convicted in April of the premeditated murder of Ms Wall, 30 on his submarine and dismembering her body.

The Danish prosecutor’s office tweeted Madsen would “solely” appeal the life  sentence handed down by the Copenhagen City Court, and not the murder conviction.

Defence lawyer Betina Hald Engmark told Denmark’s TV2 the appeal could not be interpreted as an admission of guilt.

Madsen “doesn’t confess murdering Kim Wall but that he would like the case to be over with — also for the sake of the relatives and witnesses”, Ms Engmark said.

In Denmark, the sentence range for murder is between 15 years and life.

Kim Wall’s body was found strangled and decapitated. Photo: AAP

Madsen was found guilt on April 25 of murder, sexual assault and the dismembering of Ms Wall.

The court ruled unanimously Ms Wall’s murder on August 11 last year  was sexually motivated and premeditated because Madsen brought along tools he normally didn’t take when sailing.

“After a total assessment, the court finds that the defendant murdered Kim Wall,” Judge Anette Burkoe said.

The court decided that Madsen had “dismembered the body to conceal the evidence from the crime he had committed,” she said.

Madsen admitted to dismembering the Swedish journalist’s body and dumping her body parts in the sea, but had denied murdering or sexually assaulting her.

Madsen was accused of “sexual assault without intercourse, of a particularly dangerous nature” in relation to the 14 interior and exterior stab wounds investigators found to Ms Wall’s genitals.

He claimed Ms Wall died from breathing exhaust gases that had leaked into the submarine due to a technical error while he was on the deck preparing to submerge.

Prosecutors said Ms Wall died either by strangulation or having her throat cut.

Forensics have not been able to confirm nor deny either allegation.

“The explanation is not credible and is not consistent with the following decision to dismember the body,” the judge said, noting that the jury found the murder had been planned.

Ms Wall was a freelance journalist whose work had appeared in Harper’s Magazine, The Guardian, The New York Times, Foreign Policy, the South China Morning Post, The Atlantic and TIME.

No date for the appeal has been set.

-with wires