The cause of the explosion, which occurred around 10:15 a.m., was not immediately clear. The state-run broadcaster TRT and the independent Dogan News Agency reported that the authorities were investigating the attack as a suicide bombing.
Istanbul’s historic Sultanahmet square is a major tourist attraction in Turkey’s second most populous city.
Meanwhile, tourists from Norway and Germany are said to have been wounded in the attack.
This is the second huge explosion in Istanbul, according to media reports.
No group has so far claims responsibility for the attack.
More details to be updated…