ISTANBUL?-- Turkey declared a day of national mourning on Sunday for the victims of twin bombing attacks that hit central Istanbul overnight and left 38 dead.

Flags are being flown at half mast across the country, and residents laid carnations at the bombing sites near a stadium in the district of Besiktas.

At a press conference, Interior Minister Suleyman Soylu put the latest death toll at 38, including 30 police officers, seven civilians and an unidentified person.

Another 155 were wounded in the attacks, one involving a bomb car while the other a suicide bomber, with 14 in critical condition.

Early in the morning, the minister said 29 were killed, among them 27 police, and 166 others wounded.

Soylu said indications are pointing to the outlawed Kurdistan Workers' Party being behind the attacks, which resumed fighting with government forces last year and has targeted police and military posts in Istanbul in the past months.

The blasts on Saturday night befell one and half an hour after a football match ended in the stadium.

The authorities believed that 300 to 400 kilograms of explosives were used in the attacks, press reports said.

The heaviest casualty was caused in the first attack in which a moving car was detonated, directly targeting riot police on duty.

Forty-five seconds later, a man blew himself up in Macka Park just across the stadium, killing four police and one civilian, according to Turkey's Deputy Prime Minister Numan Kurtulmus.

Though Istanbul has come under a spate of deadly attacks over the past year, a 20-year-old man who was on a bus when the attacks occurred, said he was traumatized.

The bus driver locked the doors, fearful that the attackers could take his vehicle.

"I was so in panic and I opened the door of the bus by kicking it hard," he said. "And I started to run like a crazy man without knowing where I was heading."

The roads leading to the bombing sites were closed in the morning and reporters were not allowed to pass.

Turkish President Recep Tayyip Erdogan, meanwhile, has cancelled his trip to Kazakhstan slated for Sunday and Monday.