Foreign tourists are said to be among those killed and injured in a suicide attack in Istanbul’s main tourism district. Turkish officials say at least 10 people - nine of them Germans - were killed and 15 others injured.
Police and ambulances were quickly on the scene of the blast. The powerful explosion heard across much of the city struck late morning in Istanbul’s Sultanahmet district the main tourism quarter of the city.
Turkish President Recep Tayyip Erdogan condemned the attack.
“Turkey is a top target for all terrorist groups in the region," he said, adding that “Turkey is fighting against all of them equally."
Turkish Prime Minister Ahmet Davutoglu said the attack is believed to have been carried out by Islamic State.
Speaking after the an emergency security meeting he pledged to fight the militant group until it no longer “remains a threat” to Turkey or the world.
"Our fight against Daesh (an arabic acronym for Islamic State) that carried out this attack will continue with determination. We will not take a step back in our fight against Daesh, our resolve will continue as in our fight against all terrorist organizations," he said.
Known details of the attack were given a news conference following the emergency meeting of senior ministers and intelligence chiefs.
The bomber was identified as a 28-year-old described as of Syrian origin, and most of those killed and injured were foreign nationals.
Turkey's state-run news agency said Davutoglu spoke on the phone with German Chancellor Angela Merkel to express his condolences.
Speaking to reporters in Berlin, Merkel condemned the attack, saying that the “international terrorism is once again showing its cruel and inhuman face.”
Local media, citing security officials, say the Islamic State is the chief suspect behind the attack.
Although the group never claimed responsibility, IS militants were blamed last year for two suicide attacks that killed more than 130 people, including one in the capital, Ankara.
The government has been criticized by the opposition and its allies for failing to crackdown hard enough on the jihadist group, instead focusing attention on its battle against the Kurdish rebel group the PKK, a charge it strenuously denies.
Observers say Kurdish rebels could also be a suspect, Turkish security forces are carrying out a major crackdown across towns and cities in the predominantly Kurdish southeast.
A splinter Kurdish group called TAK claimed responsibility for a mortar attack last month on Istanbul’s second largest airport.
WATCH: video from the scene
The Sultanahmet neighborhood is Istanbul's main sightseeing area and home of the Topkapi Palace, Blue Mosque and Hagia Sophia museum.
Witness Ali Hakan Ataman said it was a big explosion. "I was in a shock for a while right after it happened. Blood and flesh were spattered on us and I am sure I saw six or seven people laying on the ground dead..." he said.
Another witness, Erdogan Salihli, said people went briefly silent right after the blast. "As people were trying to figure out what really happened the cries of people at the scene was very tragic," he said.