Other security sources said a KDP local meeting was in progress at the time of the attack.
It was the second suicide attack in Kurdish areas of the north in four days.
Makhmur is just south of the autonomous Kurdish-controlled areas, but it has a substantial Kurdish population.
The blast also killed the police chief and damaged the mayor's office, officials said.
Ziryan Othman, the health minister of the Kurdish regional government, said at least 30 people were killed and 115 were wounded, including the city's mayor, Abdul Rahman Delaf, who also is a prominent Kurdish writer, and the director of the KDP office.
The attack occurred four days after a truck bombing in Arbil, the capital of the Kurdish self-governing region, killed at least 15 people and wounding more than 100.