At least one policeman has been killed in a car bomb blast near a police headquarters in the south-east Turkish city of Gaziantep, officials say.
Nineteen police and four civilians are reported to have been injured by the early-morning explosion.
The blast was heard several kilometres away, CNN Turk TV reported.
Turkey has been hit by a series of deadly blasts over the past year, linked either to Kurdish militants or so-called Islamic State (IS).
Ankara, Istanbul and Bursa are among cities that have been targeted by suicide bombings.
Some reports said gunfire was heard after the blast, which occurred at about 09:30 local time (06:30 GMT). There was no immediate word on who is behind the latest blast.
The police building is close to several government offices, including that of the governor and mayor, the AP news agency said.
Gaziantep, which is near the Syrian border, is known to have several IS cells.
In another development, Turkish police detained four suspected IS members in Ankara, the Anadolu news agency reports.
The four were thought to be preparing to launch an attack there during Sunday’s May Day parades.
Meanwhile Istanbul police used water cannon and tear gas to disperse protesters trying to stage a May Day rally in Taksim Square, the scene of violent anti-government protests in 2013.
More than 25,000 police have been deployed there for May Day.
Separately three Turkish soldiers were killed and 14 others wounded in an attack that the army blamed on Kurdish militants of the PKK.
An army statement said the attack took place in Mardin province, where the army has been conducting a military operation against the PKK. (BBC)