The suicide bombing of the Indian Embassy in Kabul is the deadliest attack in the Afghan capital since the US forces toppled the Taleban Government in 2001. It is also a vicious warning not only of the growing strength of the insurgency but also of the undeclared struggle for influence over their northern neighbour by both India and Pakistan.

For centuries, India has been preoccupied with security on its northwest frontier - the route by which so many invasions came. The British, too, spent money and blood guarding this strategic gateway. After independence, both Pakistan and India saw strategic advantage in denying each other control of Afghanistan, and each has long regarded influence in Kabul as a matter of vital national importance. Their proxy war has contributed to instability of the region. It has been costly to themselves: the lawlessness of Pakistan's frontier provinces has been encouraged by the free movement of warlords and religious extremists across the border; and India lost four embassy staff, including its defence attaché, among the 41 victims of yesterday's blast.

The Taleban have strong motives for targeting India. Many have lived in exile in Pakistan, where they absorbed not only the visceral hostility to India but also the fanaticism of those who see the ousting of India from Kashmir as a cause for Islamic Jihad. Pakistan was the main backer of the Taleban from their takeover in Afghanistan in 1986 until they were defeated by the allied coalition in 2001, when Islamabad officially dropped its support as a result of intense US pressure. Taleban insurgents are deeply suspicious of Indian support for President Karzai, who spent time in exile in India. India's close involvement in reconstruction is seen as underpinning the Western-backed Government and in recent months there have been frequent attacks on Indian offices and projects around the country.

The attack comes both when Islamabad and Delhi remain committed to their steady rapprochement. Neither side has an interest in a proxy war or instability in their northern neighbour. But the confused political situation in Pakistan after this year's elections and the strong suspicions that rogue elements of the ISI, Pakistan's powerful security service, remain unreconciled to the break with the Taleban will reinforce the suspicions of many in Delhi and Kabul about Pakistan's motives and policies in Afghanistan.

India announced yesterday that it would not be deterred by this attempt to sabotage its relations with the Afghan Government. But like the Nato countries providing troops for the International Stabilisation Force, it will be alarmed by the Taleban's growing use of suicide bombings. Though failing in the field, the Taleban have studied the example of Iraq and clearly understood the importance of switching to urban terrorism, especially in the capital: the embassy attack was the sixth suicide attack in Kabul this year. Especially after the recent government parliamentary victory in salvaging the US-India nuclear agreement, India is seen by Islamists as a partner of the West, both politically and strategically. All the more reason, therefore, for the West to support India's role in underpinning the Kabul Government and help it to resist the common threat of Taleban terrorism.