The attorney representing convicted Soviet spy Marcus Klingberg said he would continue efforts to secure his client’s early release.
The Israeli High Court of Justice rejected a petition on the matter.
Lawyer Avigdor Feldman had cited his client’s poor health as the reason for release.
Klingberg, 78, has served 13 years of a 20-year sentence. He told the Israeli daily Ha’aretz last week that he would rather die than serve out his complete sentence.
The court said Klingberg could not be freed because he still presented a security threat to the state.