ISTANBUL, Turkey, (AP) – Turkish police thwarted a bomb attack in Istanbul on Monday, arresting a 25-year-old man with explosives in his backpack outside a subway station, the city’s governor said.

The man was carrying more than seven pounds of plastic A-4 explosives when he was arrested in the Sisli district, one of the most crowded areas of the city, Turkish news agencies reported.

The motive was unclear, as was whether it was to have been a suicide attack.

Gov. Muammer Guler said it was certain that the man was planning to carry out a bombing but that police had not yet determined the intended target.

He said a man with suspected ties to the suspect was also arrested, but he did not elaborate.

Guler said police raided an apartment believed to be used as a safe house and seized more explosives and various equipment that could be used to set off a bomb. He said a woman and two children living in the apartment were being questioned.

Police chased the would-be bomber, Guler said. “He may be a member of a separatist terrorist organization,” Guler said, adopting a euphemism Turkish officials use to refer to the separatist Kurdistan Workers’ Party, or the PKK.

Militant Kurdish, leftist and Islamic groups have carried out bombings in big cities and in resort towns in Turkey. In May, a 28-year-old man convicted of membership in a militant leftist group blew himself up in Turkey’s capital, killing six people and injuring dozens.