JAKARTA, Nov. 23 (Xinhua) -- The Indonesian authorities have said they would verify the authenticity of a threat conveyed by an Indonesian radical group affiliated to the Islamic State (IS), and prevent the threat from spreading further.

The threat to occupy the presidential palace and attack the Jakarta police headquarters was clearly conveyed via a video posted on Facebook on Sunday.

The video, entitled "The Call of Commander Abu Wardah Asy-Syarqi," depicts a man delivering a speech with a black IS flag on his left side.

"We are the troops of Islamic State, warning you. Whether you believe it or not, like it or not, willing or not, by God's consent this black flag will wave on top of the presidential palace and we will destroy the Jakarta police headquarters," the man said in part of his speech showed in the video.

The man was allegedly Santoso, the notorious leader of a radical group based in Poso Central Sulawesi province that was responsible for a series of attacks against police stations in the province and the killing of dozens of policemen.

Responding to the threat in the footage, Jakarta Police Chief Inspector General Tito Karnavian said that police would verify the authenticity of the video.

In addition, police serving in the capital have been told to be on alert and closely monitor radical cells' strongholds in Jakarta and its outskirts.

"There are several cells here in Jakarta, but we are yet to have credible information about their attack plans or their capability in doing so," Tito said in his office on Monday.

He added that he had enhanced communications with police officers supervising Jakarta outskirt areas of Bogor, Depok and Bekasi to tighten the surveillance against suspected movements of radical groups' cells in those areas.

In a separate occasion, Head of Indonesia's National Counterterrorism Agency (BNPT) Saud Usman Nasution said his office had carried out several moves after the broadcasting of the video.

Besides investigations to find out the authenticity of the video and identity and motive of the person who uploaded it, BNPT have also coordinated with the Communication and Informatics (Kominfo) Ministry to stop the video from spreading further.

The law enforcement agencies would take measures against those involved in the case, Saud said here on Monday.

Indonesia's Bali and Jakarta have witnessed several terror attacks in the past decades that have killed hundreds of people.