BALI police are investigating a threatening letter that claimed Islamic State militants were ready to bomb the island.

The letter has also prompted police to tighten security across Bali’s seaport, airport and crowded areas that are popular with tourists.

The note was delivered to a government office in northern Bali just days after the Jakarta attacks that left eight people dead, including four civilians and four terrorists.

According to reports, the note stated: “Our members are currently present in Denpasar and Singaraja” and threatened “to blow up these cities in the name of Allah.”

“Our members are currently present in Denpasar and Singaraja,” it said. The letter also warned they would “attack shopping centres, offices and tourism destinations”.

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Buleleng police chief Heri Heriyadi confirmed the letter had been delivered to the local government office at Buleleng before 9am.

“When the letter was opened by administration staff the situation turned quite chaotic,” he said.

“It was a threatening letter, one of our team was there, saw the letter and the ruckus, they immediately took the letter and witnesses to police station, so we can do an immediate follow up.”

Police are yet to identify the man who walked into the Buleleng district government office in the north of the island, but have questioned several witnesses to obtain a description of him.

“We are now investigating the letter,” said Bali police spokesperson Hery Wiyanto.

“We have questioned several witnesses, mostly staff of the Buleleng subdistrict office where the letter was sent.

“We are informed that the man brought the letter wearing helmet and glasses, so, it doesn’t clearly show his face. He drove a motorbike.”

Wiyanto said Bali was now under tight security.

“We are tightly monitoring Bali’s entrance, the seaport and airport,” he said.

“We are deploying more personnel in seaport, airport, and many crowded areas, including areas where many foreigners gather. We are also intensifying patrols.”

Wiyanto said he believed the letter was sent to spread terror.

“I think it is aimed to spread terror,” Wiyanto said.

“It may be done by people only for fun, but may also be serious. So, we still have to be vigilant.”

Despite the terror threat being made, he said Bali was currently “safe”, with locals and foreigners able to do normal activities.

Islamic State claimed responsibility for the gunfire and seven explosions, including one attack at a Starbucks near the United Nations building, that took place in central Jakarta on Thursday last week.

The death toll now stands at eight, including four civilians.

Rallies were held across Indonesia yesterday to condemn the terror attack and in Indra Maya in West Java, a crowd of locals took to the streets.

Residents there do not want their town to be remembered as the former home of 25-year-old Ahmad Muhazan, the Starbucks suicide bomber.

Muhazan’s body was due to be brought to Indra Maya for burial but a group of locals marched through town with a banner that read: “We reject the corpse of the terrorist”.

A local cleric was among the crowd.

“The grassroots have rejected the corpse and moreover the educated people like the scholars, students, clerics and the community elders, they are clearly rejecting the corpse because his deed violates law and religion.”

Another rally took place in Purwokerto, Central Java, where the local branch of Indonesia’s largest Islamic youth movement marched with signs saying, “Go to hell terrorists” and “Let’s reject the caliphate — it damages Indonesian unity”.

The Australian government website smarttraveller.com.au advises Australians to exercise a high degree of caution in Indonesia, however the overall level of advice has not changed since the attacks.