Key Points:

The most alarming aspect of this week's horrific assault on Mumbai was the scale of the terrorists' ambition. The military-style attack was not only well planned and well orchestrated but, unusually, embraced an array of targets.

Residents of India's financial capital bore the brunt of onslaughts at the main railway station, the airport, a cinema and the city's southern police headquarters.

But, for the first time in India, Americans and Britons were specifically targeted as hostages were sought in attacks on two luxury hotels and a cafe frequented by tourists.

On the one hand, the breadth of the destruction obscured the terrorists' objectives. On the other, however, it confirmed that terrorism is as much, if not more, of a scourge as ever.

That harsh reality was emphasised by the method of attack. The Islamic militants, who are believed to have slipped ashore from boats, used automatic weapons and grenades, rather than the bombs employed in previous atrocities.

That meant the number of casualties did not approach the 190-plus Mumbai commuters who were killed when a series of seven blasts ripped through trains and stations in July 2006. But a death toll standing at more than 130 and the pictures of flames shooting from iconic landmarks spoke eloquently of the impact of this less sophisticated approach, and of a new tactical fluidity.

Analysts have their hands full attempting to identify the terrorists. A previously unknown group, the Deccan Mujahideen, has claimed responsibility, and there are suggestions the motive lies in contested claims to Kashmir or the treatment of India's 140-million Muslim minority.

The country's increasingly close ties with the United States are also a matter of contention. But the assault bore some of the hallmarks of an al Qaeda operation, notably simultaneous attacks and the targeting of Westerners and the hotels used by them. Significant al Qaeda leaders have been struck down by American drones, but if nothing else, the group clearly remains an inspiration for terrorist cells.

The degree of danger, and its global nature, had been re-emphasised even before the Mumbai carnage. The United States is on heightened alert as the inauguration of President-elect Barack Obama draws near.

Al Qaeda's number two, Ayman al-Zawahiri, has termed Mr Obama a "house Negro", and there is every incentive to undermine the new administration through an attack on the US. Further evidence of the threat was provided last month by the Australian

Security Intelligence Organisation, which, in its annual report, said Australia had only narrowly escaped terrorist attacks on its soil. The spy agency said that militant Islamic jihadists would remain its most potent enemy for the foreseeable future.

Terrorist organisations must, because of their inherent weakness, select soft targets. Australia and the US do not fit into that category. India, however, is more vulnerable than most.

It is open, particularly to intrusion from Pakistan, which remains a haven for terrorists. Densely populated and chaotic cities also provide a ready potential for surprise, as in the case of the Mumbai attack. Other Indian cities have also been assaulted in the past few months.

The world has reacted with anger to the horrors perpetrated in Mumbai. There was a similar reaction in September when a huge truck bomb devastated the heavily guarded Marriott Hotel in Islamabad, killing up to 60.

South Asia is bearing the brunt of terrorism at a time when Pakistan's relations with the US remain fraught. Repairing that relationship and restoring stability to the region through the elimination of extremism must be the top foreign-policy priority for the incoming American administration. The large-scale assault on Mumbai reinforced just how difficult that will be.