A bomb attack outside the police headquarters in Turkey's southeastern city of Gaziantep has killed two policemen and injured 22 others, officials say.

There was no immediate claim of responsibility for Sunday's attack, which happened about 60km from the Syrian border.

Security sources, however, said police raided the home of a man suspected of links to the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group 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, the daily Hurriyet reported.

One of the cars drove off, while the second exploded, according to the newspaper.

'Extremely nervous'

Reporters were told that there may be the threat of another attack.

Al Jazeera's Stefanie Dekker, reporting from the scene, 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 who approaches.

Later on Sunday, 10 soldiers were wounded in a bomb attack in the largely Kurdish southeastern town of Dicle, Turkish security officials said.

Ambulances went to the scene, about 65km north of Diyarbakir, the region's biggest city.

In the same region, three soldiers were killed and 14 others wounded in an earlier attack by Kurdish fighters during a military operation in the town of Nusaybin, Turkey's army said in a statement.

A May 1 rally in the city of Adana was cancelled earlier on Sunday as a result of a suicide-bomb threat.

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," she said, referring to the outlawed Kurdish armed group.

"Finally, you have the spillover of the Syrian war."

Target of attacks

Since the emergence of ISIL 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 that the pair was planning suicide bombings in Gaziantep and other Turkish cities, according to the governor's office.

Last December, Turkish counterterrorism 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 PKK fighters.

Artillery attacks

Kilis, another Turkish border town only 56km away from Gaziantep, has been the target of several artillery attacks in the past weeks.

Official sources say a total of 17 people have been killed in Kilis this year from repeated rocket attacks.

"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."

Turkey's largely Kurdish areas have been hit by waves of violence in clashes between government security forces and PKK fighters after a ceasefire fell apart last July.

"It is a tense Turkey nowadays. A low-intensity civil war is going on in the southeastern provinces," Yavuz Baydar, a Turkish columnist, told Al Jazeera from Istanbul.

"As for the oppositional liberal parts of society in the urban areas, they believe their demands are not being met, and not even being listened to, by the government. This tension has been spreading across the country."