This attack is a bloody reminder for Indonesia of the dark pools of intolerance hidden among a people who are mostly open and welcoming.

A rampage on the streets of Jakarta - though shocking - comes as no great surprise. Warnings have been growing for more than a year that the insidious hate preached by Islamic State from long distant Syria and Iraq had found receptive ears in Indonesia.

Up to 700 Indonesians are estimated to be fighting with Islamic State, and while the true number is likely to be fewer, there are grave fears about the mayhem any of these fighters who return home may seek to create.

Whether this assault on Thursday was indeed an Islamist attack, we don't yet know. The police in Indonesia were quick to blame Islamic State, but in the years after September 11, 2001, they also blamed al-Qaeda as a scapegoat for many locally spawned plots.

As it happens, just hours before, Al Qaeda's 's leader Ayman al Zawahiri coincidentally urged his followers to strike in South East Asia.

What is clear is that the method fits the pattern of bloody mayhem Islamic State has tried to foment - killings to sow fear, anywhere and everywhere.

But this rampage, at least as it has initially unfolded, lacked the deadly sophistication of the Bali bombings or Australian embassy attack, where destructive and complex homemade explosive wrought such havoc.

Not to diminish the terrible cost here, with at least seven dead, including a policeman. But it suggests weakness on the part of the terrorists, not strength.

The extremists appear to have posted false reports on social media of other attacks elsewhere in the city, in what may have been a bid to divert police attention or simply create more panic.

It seems doubtful that this attack could have been directly orchestrated in Syria, at least in the formal sense of a terrorist mastermind directing the attack from afar.

And that is significant as it could increase the chance of rounding up suspects to prevent further attacks.

The police claimed to have warning of a "concert in Jakarta", which sounds a similar code to that used in the past, when terrorists used the word  "wedding" to signify a suicide bombing.

Early reports indicated about half a dozen attackers threw grenades from motorcycles and firing guns, but this has yet been confirmed.

The targets appears to have international links, a Starbucks cafe and building home to a United Nations office, but not in the wealthiest or most overtly Western zones of the city.

That might also be a consequence of the often heavy-handed crackdown by Indonesian police and security agencies to defend obvious targets and an attempt to evade scrutiny.

The pressure on Indonesia as a nation now is to withstand the poison of intolerance, to maintain its open and welcome demeanour, and to prevent the terrorists  from achieving their goal of division by fear.