Security sources in Van said initially that the casualties occurred when an explosive device was hurled at a municipal police vehicle parked in front of a sports centre near the governor's office on Thursday.
But Mustafa Yavuz, Van's deputy governor, told the Anatolia news agency that they suspected a suicide bomber was behind the blast.
"We believe it was a suicide bomb attack, but a definite conclusion will be reached only after the investigation is complete," he said.
Police identified two of the victims and were investigating the identity of the third, who was standing near the vehicle at the time of the blast and whose body was mutilated by the impact, Yavuz said.
Four of the wounded were in serious condition, he said.
It was not immediately clear who was behind the attack, but rebels of the outlawed PKK (Kurdistan Workers' Party), which has been fighting the army in the east and southeast of the country since 1984, are known to be active in the area.