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 7 pounds of A-4 plastic explosives when he was arrested in the Sisli district, one of the most crowded areas of the city, Turkish news agencies reported.

Though Governor Muammer Guler said the man was surely preparing for a bomb attack but said police were not yet able to find out what his target had been.

Guler said police launched a raid on an apartment believed to be used as a safe house and seized more explosives and various mechanisms that could set off a bomb. Another man at the apartment was arrested after a chase, Guler said, and was suspected of membership in an unspecified terrorist organization.

Militant Kurdish, leftist and Islamic groups have carried out bombings in big cities and in resort towns in the past.

In May, a 28-year-old once convicted of membership in a militant leftist group blew himself up in Turkey's capital, killing six people and wounding dozens.