Flyers and letters warning that bomb attacks will be carried out at a number of locations in Batam and Bintan in the Riau archipelago have surfaced, an Indonesian news website has reported.
Text messages with the warning have been circulating and photos of the purported flyer have appeared on social media, but it is not known whether or not they are a hoax.
According to Batam Today, the flyers claim that attacks would occur at the Batam Center Ferry Terminal and Nagoya on the island of Batam, as well as Bintan Telani and Tanjung Pinang on the island of Bintan.
The attacks are reportedly meant to target travellers from Johor and Singapore.
The letters also mention that the militants planning the attacks had arrived in Riau two weeks ago.
Tanjung Pinang district police chief Kristian Siagian confirmed the existence of the flyers and said that investigations by the authorities are ongoing.
"In the aftermath of the bomb attack on the police headquarters in Solo, we have increased security measures in Tanjung Pinang, especially around vital targets such as police headquarters and ferry terminals," he said.
Meanwhile, Bintan police chief Febrianto Guntur Sunoto urged residents to remain calm.
"We hope that residents do not panic. We have acted on the information and law enforcement officers have increased security levels here, especially at the locations that were mentioned in the flyers," he said.
On July 4, Singapore's Ministry of Foreign Affairs (MFA) issued a travel advisory due to the recent spate of terrorist attacks on civilian targets such as international airports and areas popular with tourists and locals.
Citing the Dhaka and Baghdad attacks, MFA advised Singaporeans to eRegister their whereabouts when travelling.