Fighting between Kurdish and Islamic State group militants in Syria has spilled over into Turkey in recent months. Above, Kurdish protesters clash with Turkish riot police in Istanbul, Oct. 8, 2014. Ozan Kose/Agence France-Presse/Getty Images

Kurdish militants have claimed responsibility for the assassination of an Istanbul supporter of the Islamic State group, local media outlets reported Thursday. The attack came as fighting between Kurdish and Islamic State militants in Syria was threatening to spill over into neighboring Turkey.

The man killed, Mursel Gul, a soap salesman, was shot late Wednesday night in a setup by members of a group affiliated with the outlawed Kurdistan Workers’ Party (PKK) in Istanbul’s Sultangazi district. Police said Gul was shot four times as he delivered an order of soap to the perpetrators, who posed as salesmen. In a statement, the PKK’s youth wing said it had been tracking Gul for at least three months.

"We will continue our operations against the ISIS gang and have identified many of them and will execute and punish them," the group said in a statement, according to Al Arabiya. [The Islamic State group is also known as ISIS or ISIL.]

Police said Gul praised ISIS on social media and had crossed back and forth between Turkey and Syria, according to Hurriyet Daily News. The youth movement said Gul held a significant position in ISIS, a claim that has drawn skepticism following an antiterror police investigation that has yet to reveal a connection between Gul and the militants, Al Arabiya said.

The assassination came as Kurdish militants from the PKK staged a series of retaliatory attacks following Monday’s deadly suicide bomb blast at a cultural center in the predominantly Kurdish southern town of Suruc, Turkey. More than 30 people were killed in the bombing. Most of them were young activists with the Federation of Socialist Youth Associations who had volunteered to help rebuild Kobani, a Kurdish city just over the Syrian border that was the site of intense fighting last year and earlier this year. The center has regularly hosted international journalists, left-wing activists and Kurdish militants.

Fighting in Syria has threatened to upend Turkey’s relative progress in peace talks with Kurds in recent years. Late last year, Kurdish activists staged protests across the country, calling on the Turkish government to allow Kurdish fighters living in Turkey to enter the Syrian city of Kobani as ISIS militants laid siege to the city, and have generally expressed anger over the Turkish government's slow support in aiding the fight against ISIS.

On Wednesday, the PKK reportedly also shot dead a 33-year-old man at his home in southern Turkey who they said was a sympathizer of ISIS. Kurdish militants also claimed responsibility in the killing of two Turkish police officers.