Indonesian police have made four arrests in connection with the fatal stabbing of a policeman in Medan by two assailants early yesterday morning.
A search of one of the assailants' homes uncovered an Islamic State in Iraq and Syria (ISIS) flag among his possessions, indicating that he could be a supporter of the terrorist group, according to national police spokesman Setyo Wasisto.
The police conducted raids across Medan, the capital of North Sumatra province, after the stabbing of the policeman who was on sentry duty at the North Sumatra Police Headquarters.
The attack took place at 3am yesterday, just as millions of Indonesians were about to celebrate Idul Fitri and mark the end of the Muslim fasting month of Ramadan.
The assailants set on officer Aiptu Martua Sigalingging at a guard post and stabbed him to death.
Mobile Brigade police commandos who rushed to the scene opened fire, killing one assailant and injuring the other, after they refused to heed a warning to stop.
North Sumatra police chief Rycko Amelza Dahniel said the wounded man, identified as Medan resident Syawaluddin Pakpahan, had travelled to Syria intending to join ISIS.
Inspector-General Setyo said the duo had been instructed to carry out the attack by Bahrun Naim, an Indonesian who is now among the ranks of ISIS and said to be behind a recent string of attacks in Indonesia, and a foiled plot targeting Singapore last year.
"They were asked to mount amaliyah (attacks) with whatever they had," he said. "If they had no bombs, then use whatever."
Insp-Gen Setyo said counter-terrorism investigators are trying to establish what links the assailants had with local terrorist groups.
"Some time ago, Densus 88 arrested three people for planning such an attack. It seems that their group, or other cells, managed to send two others to attack the North Sumatra police," he added.
Densus 88 is the police counter-terrorism unit that arrested 41 suspects following the May 23 suicide bombings in Kampung Melayu, East Jakarta, which killed three policemen.
Officer Aiptu is the fourth Indonesian policeman killed in a terrorist attack since then.
Apart from five of the 41 who were released, the rest have links to the Jemaah Ansharut Daulah (JAD) terror network, said the police.
Indonesia has been hit by a series of attacks since four JAD militants laid siege on downtown Jakarta in January last year.
ISIS had claimed responsibility for that attack as well as the Kampung Melayu bombings.
Institute for Policy Analysis of Conflict director Sidney Jones said the Indonesian police are often targeted by militants because they are responsible for arresting and sometimes killing them.
The Indonesian police have been on high alert since last week over fears of terror attacks during the Muslim holidays.
But stabbings carried out by small groups or "lone wolf" terrorists have posed a major challenge not just for the Indonesian police, but also police forces and counter-terrorism agencies around the world.
The Medan incident came just days after a similar knife attack at an airport in the US state of Michigan, where a police officer was stabbed in the neck by a Canadian man who was heard yelling "Allahu Akbar" (God is great), before he struck.
It is the ninth incident this year which involved the stabbing of police officers or innocent civilians in public, beginning with the car- and-knife attack on Westminster Bridge in London on March 22.