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 3Â½ kilograms (7 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. Governor Muammer Guler said it was certain that the man was planning to carry out a bomb attack but that police had not yet determined the intended target. He said a man with suspected ties to the suspect was also arrested but 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.