A South Korean appeals court has increased the jail term for former President Yoon Suk Yeol on charges linked to his short-lived 2024 martial law declaration to seven years.

A lower court sentenced Yoon to five years in prison in January after clearing him of some of the charges, but a court has found Yoon guilty of more charges following his appeal, including mobilising the presidential security service to prevent authorities from arresting him.

"In trying to stop authorities from executing an arrest warrant by use of force, Yoon committed acts that are unacceptable in a society of law and order," the Seoul High Court judge said.

The 65-year-old former prosecutor, who was impeached and removed from office last year, was also found guilty of charges that included fabricating official documents and failing to follow the legal process required for martial law, which has to be discussed at a formal cabinet meeting.

The decision, the first by a special court division set up to handle cases linked to the martial law bid, was televised.

Prosecutors were seeking a 10-year prison term, accusing Yoon of betraying public trust, undermining the constitutional order and using state resources to privatise public power.

Yoon had appealed the lower court's decision, saying it ignored evidence that emerged during the trial and misinterpreted the facts.

On Wednesday, his lawyers said he would appeal to the Supreme Court, calling the appeals court's ruling "incomprehensible" and that the court erred in applying rigid legal principles to what could be considered political acts.

The case is among the eight trials Yoon faces since his removal last April. He has been in jail since July.

Among the other trials, Yoon was sentenced to life in prison in February for masterminding an insurrection tied to his imposing martial law in 2024.

Yoon has denied wrongdoing.