A Kurdish militant group has said it carried out a car bomb attack in central Istanbul on Tuesday that killed seven police officers and four civilians.
The Kurdistan Freedom Falcons (TAK) said the attack was in revenge for Turkish army operations in the Kurdish-dominated south-east.
It has warned foreign tourists that Turkey is no longer safe to visit.
The TAK is regarded as a splinter group of the Kurdistan Workers' Party (PKK).
"The action was carried out to counter all the savage attacks of the Turkish republic in Nusaybin and Sirnak and other places," a TAK statement said, referring to the areas in the south-east where the military has been confronting Kurdish rebels.
"We again warn foreign tourists who are in Turkey and who want to come to Turkey: Foreigners are not our target but Turkey is no longer a safe country for them. We have just started the war."
It described Tuesday's attack as a "sacrifice action", terminology which correspondents say implies it was a suicide bombing.
The TAK has also claimed responsibility for two attacks that killed dozens in the capital Ankara in February and March.
It also claimed responsibility for an attack in April in Turkey's former Ottoman capital of Bursa, when a suspected female suicide bomber injured 13 people.
The TAK statement also strongly denounced President Recep Tayyip Erdogan's Justice and Development Party, accusing it of waging a "wild war" against Kurds.
Recent attacks in Turkey
- June 2016: 11 people killed in a car bomb attack on a police bus in central Istanbul
- March 2016: 35 people killed by Kurdish militants in Ankara; four dead in a suicide attack in Istanbul
- February 2016: 28 killed in military convoy in Ankara
- January 2016: 12 German tourists are killed in a suspected IS suicide bombing in Istanbul
- October 2015: More than 100 people are killed in a double suicide bombing at a peace rally in Ankara
Turkey's south-east exploded into violence last year when the peace process which began in 2012 between the government and Kurdish rebels collapsed.
The rush hour car-bomb on Tuesday morning was directed at a police vehicle in Istanbul and injured scores of people.
It was the fourth major attack in Turkey's largest city this year.