ISTANBUL --A small bomb left on the side of a road in central Istanbul exploded late Saturday, slightly wounding three people, Turkey's state-run news agency reported.

The bomb, which was designed to create a loud noise, was left near an overpass in the city's central Mecidiyekoy district, the Anadolu Agency reported. There was no immediate claim of responsibility.

Three people were hospitalized, but were not in serious condition, the report said.

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The explosion came hours after the United States warned its citizens about "credible threats" to tourist areas in Turkey, especially around public squares and docks in Istanbul and the Mediterranean beach resort of Antalya. The emergency message from the U.S. Consulate urged citizens to exercise "extreme caution" near those locations.

Turkey has been hit by six major bombings since July that have killed more than 200 people, including a suicide bombing in Istanbul last month blamed on the Islamic State of Iraq and Syria (ISIS) that killed two Israeli-Americans, another Israeli and an Iranian man.

Kurdish militants linked to the outlawed Kurdistan Workers' Party, or PKK, have claimed responsibility for two deadly attacks in the capital Ankara in February and in March.