A bomb attack outside the police headquarters in Turkey's southeastern city of Gaziantep has killed two policemen and injured 22 others, officials said.
There was no immediate claim of responsibility for Sunday's attack, which happened some 60km from the Syrian border.
Security sources, however, said police raided the home of a man suspect with links to the Islamic State of Iraq and the Levant group (ISIL, also known as ISIS) after the attack. The suspect's father was detained.
Turkish media reported that an explosive-laden vehicle blew up next to the safety barriers at the entrance of the city's main police station.
Two cars entered the area with assailants firing automatic weapons and police responding to the attack, daily Hurriyet reported.
One of the cars drove off, while the second car exploded, according to the newspaper.
Reporters were told that there may be a threat of another attack.
Al Jazeera's Stefanie Dekker, reporting from the scene of the blast, said police officers at the station were "extremely nervous".
"Police officers wouldn't let anyone come within 100 metres of the police headquarters," she said. "They are literally cocking their weapons at anyone that approaches.
A May 1 rally in the city of Adana was cancelled earlier on Sunday as a result of a suicide bomb threat.
'Security threats on multiple levels'
Our correspondent said Turkey faces security threats "on multiple levels".
"It has had ISIL-linked attacks across the country, and then you also have the threat of the PKK.
"Finally, you have the spillover of the Syrian war."
Since the emergence of the Islamic State of Iraq and the Levant group (ISIL, also known as ISIS) in the summer of 2014, several Turkish cities, including Gaziantep, have been under threat.
In April, Turkish authorities detained two alleged ISIL members in Gaziantep. It was believed the pair was planning suicide bombings in Gaziantep and other Turkish cities, according to the governor’s office.
Last December, Turkish counter-terrorism units revealed that members of ISIL prepared suicide-bomb vests and other materials in a depot in the city for use in the double suicide bomb attack that killed 102 people in Ankara on October 10, 2015.
Gaziantep was also the target of several attacks before the emergence of ISIL.
In August 2012, a bomb attack near a police station in the city killed 10 people and injured 66.
Although there was no claim of responsibility, the bombs were believed by Turkish officials to be planted by the outlawed Kurdish PKK group.
Kilis, another Turkish border town only 56km away from Gaziantep, has been the target of several artillery attacks in the last weeks. Official sources say a total of 17 people have been killed in Kilis this year from repeated rocket attacks.
'Anything can happen at any moment'
"We've also had Syrian journalists shot dead, in the open streets here in Gaziantep, just a week ago because they were very critical, vocally, publicly critical of ISIL" Al Jazeera's Dekker said.
"Syrians have moved here for relative safety but it just goes to show that it isn't safe, that anything can happen at any moment."
Elsewhere in Turkey on Sunday, three soldiers were killed and 14 others wounded in an attack blamed on Kurdish fighters during a military operation in the southeastern town of Nusaybin, Turkey's army said in a statement.
Turkey's largely Kurdish southeast has been hit by waves of violence in clashes between government security forces and members of the outlawed Kurdistan Workers Party (PKK) after a ceasefire fell apart last July.
Source: Al Jazeera and agencies