JAKARTA - Indonesian President Joko Widodo on Thursday condemned the attacks in the nation's capital Jakarta and ordered the apparatus to pursue and arrest those involved as well as their network.

"The state and people must not be afraid, must not lose against such a heinous attack. I call all of the people to remain calm as everything is under control," the president said, responding to the attacks.

"We all extend a heartfelt condolence to the victims of this attack. But we all certainly condemn the act which disturbed the security of the people and launched terror to the people," President Widodo said.

The Indonesian president on Thursday decided to cut short his working visit in a town of Cirebon in West Java and ordered the authorities to pursue and arrest the attackers in Jakarta.

"I have ordered the police chief and security chief minister to hunt them in the scene or in the networks," he said.

President Widodo also called for the people to be calm as the situation is under control. "I shortcut my visit and will return to Jakarta," he said from Cirebon town, " he said at a local television in a live broadcast.

One policeman and three civilians were killed, and two other policemen were injured after gunmen attacked a traffic police post near a shopping mall here on Thursday, national police spokesman, Brigadier General Anton Charliyan told reporters.

"Three police were victims, one of them was killed and two others were injured, and three civilians were also killed," the spokesman said.

Previously, the spokesman said all the three policemen were killed.

Indonesia Police Chief General Badrodin Haiti said security in the presidential palace has been beefed up after explosions and fire exchanges with attackers at the heart of the capital city.

"Yes, there are more deployment of force (in the palace)," Badrodin said, but he did not go into details on either the number or security measures taken in the palace to respond to the attacks.

The strikes occurred after the police got warning that the Islamic State (IS) group would launch attacks in Indonesia, Brigadier General Anton Charliyan told reporters at the scene.

"It is clear that from the warning given by IS group that Indonesia will have a concert, Indonesia will be an international news," he said.

Therefore, "we have given warning too," of the possible strikes, and conducted arrests of several militants in many places in the country, said Anton.

Jakarta Police spokesman M. Iqbal said in a TV telephone interview that "The explosions were allegedly from bombs, we don't know yet. Further investigation is underway at present. Our apparatus is now combing a coffee shop building at the left side of the attacked traffic police post."

Footage broadcast by Metro TV showed that some of the explosions also took place in the front yard of the shopping mall. Another footage showed two people in white clothes pointed their guns to the street direction, and gave orders to their colleagues who followed behind.

The TV reported that at least 14 people were involved in the shootout with police. A witness said that among those killed was a foreigner.

The TV also reported that another explosion occurred in Palmerah, West Jakarta.