Özgür Yılmaz, the lawyer representing Stephen Shak Kaczynski, who was imprisoned on accusations of being a member of an outlawed leftist Revolutionary Liberation People's Party-Front (DHKP-C) involved in a recent deadly hostage situation, said on Tuesday he will appeal the ruling on Thursday.

"My client refuted all charges. I am going to appeal the arrest ruling," Yılmaz told Anadolu Agency. He added that the court had to rule on his appeal within 15 days.

Kaczynski, a 52-year-old British national of Polish origin, was taken into custody last Thursday after Istanbul police raided 38 different locations in the Okmeydanı district.

The raid came after a hostage situation last Tuesday that led to the death of Prosecutor Mehmet Selim Kiraz, for which members of the DHKP-C claimed responsibility.

Appearing before the court on Saturday, an Istanbul court ruled for Kaczynski's arrest along with four others. Kaczynski was jailed in Istanbul's Maltepe district.

Local media alleged that the British national arrived in Turkey with three different plots up his sleeve including last Tuesday's hostage taking.

Police sources talking to local media said Kaczynski had entered Turkey from Greece, adding that his bank accounts showed suspicious activity after his arrival.

His lawyer denied accusations that Kaczynski was a member of the leftist organization.

"Three questions were asked [at the prosecution office]. Those questions do not justify in any way that my client is a member of such a group," Yılmaz said, adding that Kaczynski was at an Istanbul cultural center only to spend the night.

A Foreign Office spokeswoman in London confirmed that a British national was arrested, adding: "We are offering consular assistance."

The lawyer said no British official had gotten in touch with him so far, but that "Kaczynski received a call from British officials, informing him about the legal procedure [in Turkey]."

The DHKP-C was founded in 1994. Supporting Marxist-Leninist ideology, it was mostly active as its previous iteration during the Cold War era. The group has revived its attacks in recent years.

Targeting security officials, high-profile politicians and carrying out suicide bombings, the DHKP-C is listed as a terrorist organization by Turkey, the United States and European Union.