A Kurdish militant group has claimed responsibility for the bomb attack outside an Istanbul soccer stadium that killed 38 people and wounded 155.
The Kurdistan Freedom Hawks (TAK) released a statement on its website saying that it had carried out the attacks.
TAK has taken responsibility for other deadly attacks in Turkey this year.
Meanwhile, Turkey has declared a national day of mourning after the twin blasts on Saturday night.
The bombs targeted police officers, Turkey's Interior Minister Suleyman Soylu told reporters.
He said 10 people had been arrested in connection with the "terrorist attack".
Prime Minister Binali Yildirim ordered flags to fly at half-staff on Sunday across the country and at Turkey's foreign missions.
Most of the dead were police officers. The civilian death toll was lower because fans had already left the newly built Vodafone Arena Stadium after the soccer match when the blasts occurred.
Witnesses also heard gunfire after the explosions.
"We have once again witnessed tonight in Istanbul the ugly face of terror which tramples on every value and decency," Turkish President Recep Tayyip Erdogan said.
The first and larger explosion took place about 7.30pm after the home team Besiktas beat visitor Bursaspor 2-1 in the Turkish Super League.
Mr Soylu said the first explosion was caused by a passing vehicle that detonated in an area where police special forces were located at the stadium exit.
A riot police bus appears to have been the target.
Deputy Prime Minister Numan Kurtulmus said a person who had been stopped in nearby Macka Park committed suicide by triggering explosives moments later.
This year Istanbul has witnessed a spate of attacks attributed by authorities to the Islamic State group or claimed by Kurdish militants.
A state of emergency is in force following a failed July 15 coup attempt.
Soylu acknowledged the country was struggling against "many elements" trying to compromise its fight against terrorism.
Turkey is a partner in the US-led coalition against the Islamic State and its armed forces are active in neighboring Syria and Iraq.
It is also facing a renewed conflict with an outlawed Kurdish movement in the southeast.
Reuters / AP