Vaudine England, Jakarta – Indonesian police are investigating a bomb found in a hospital bathroom in Yogyakarta, central Java, which the royal capital's reigning sultan blamed on provocateurs.

One security guard was injured when his proddings of a suspicious object at the state-run Dr Sardjito General Hospital on Tuesday triggered an explosion. The discovery comes after two other bombs were found last week on a road and in a bus in Yogyakarta – the country's most popular tourist destination after Bali.

According to experts and local leaders, the planting of bombs follows the pattern of efforts to provoke unrest in other parts of the country, with the key difference this time being the targeting of the heartland of Javanese culture. Some analysts are already linking the bombs to the raids in October on hotels in the area by groups claiming to be militant Muslims upset about the Middle East, local sin and the presence of foreigners.

Sultan Hamengku Buwono X said yesterday he had been told two weeks ago while visiting Jakarta that three suspicious characters might have arrived in Yogyakarta from the East Java town of Banyuwangi, the site of brutal unrest during the fall of former president Suharto. Ten more provocateurs were thought to be coming from Jakarta. "It is intended that Yogyakarta's image as a safe region becomes an unsafe one," the sultan said.

Such theories about mysterious "dark forces" usually focus on the alleged desire of rogue military officers and Suharto supporters to discredit the country's fragile democratic experiment and encourage calls for a return to military-backed rule. Radical Islamic groups are accused of being willing, paid tools of such groups in an unholy alliance to gain power.

Meanwhile, the Minister of Culture and Tourism, I. Gede Ardika, has concluded that a year of mob violence has taken its toll on the country's tourism industry, even though arrival figures for January to October this year are about 5 million, up 6.8 per cent on last year.

"We are still suffering from the consequences of these radical mob actions. For instance, many reservations to annual tourism and sports events as well as cruise stopovers have been cancelled," Mr Ardika said.

The world used to think the country was just going through a rough democratic transition, he said. "But once those groups started to take action directly against foreigners, they confirmed the image that Indonesia was no longer a secure place for tourists. Actually, our country is safe and we have lots of places worth visiting."