Dozens of groups, mostly based in neighbouring Pakistan, have been responsible for a string of attacks against targets in India over the past decade with two organisations, Lashkar-e-Toiba (Soldiers of the Pure) and Jaish-e-Mohammad (Army of Mohammad), regarded as the most effective and deadly.

Although there were no immediate claims of responsibility for today's bombings, Western intelligence experts had been anticipating a new wave of attacks in India by militants.

Shivraj Patil, the Indian Home Minister, said that the authorities in Delhi had been warned about an imminent terrorist operation, but did not know the time or location.

Gareth Price, the head of the Asian Programme at the Royal Institute of International Affairs, said that militant groups were hoping to harm improved relations between Manmohan Singh, the Indian Prime Minister, and President Pervez Musharraf of Pakistan, who last year signed an agreement to ease relations between the two rival states.

“In the past these attacks have sometimes provoked communal unrest between Muslims and Hindus and caused friction between Pakistan and India. That could be the purpose of these bombings today,” said Dr Price.

In December 2001, militant gunmen stormed the parliament building in Delhi, killing more than a dozen people. In the aftermath, India blamed Pakistan for the incident and the two nuclear-armed states mobilised their forces and were pushed to the brink of war.

Since then, Pakistan has taken steps to crack down on militant groups and arrest their leaders. The countries have also helped ease tensions by improving diplomatic ties, opening travel links and agreeing to put their dispute over Kashmir to one side.

But there is evidence that the militant movement has regrouped and is growing again.

After the devastating earthquake in Pakistani Kashmir in October, several Muslim groups with links to militants were allowed to mobilise to help the victims by collecting donations and organising reconstruction.

Since then there have been several attacks in India, including the bombing of a market in Delhi and explosions at a Hindu temple in Varanasi. Hours before today's bombings in Bombay, Kashmiri separatists launched a series of machinegun and grenade attacks in Srinagar, the Kashmiri capital, killing eight tourists.

Pakistan was at pains to distance itself from the bloodshed in India. President Musharraf and Shaukat Aziz, the Pakistani Foreign Minister, condemned the killings as a “despicable act of terrorism”.

The Foreign Ministry said in a statement: “Terrorism is the bane of our times and it must be condemned, rejected and countered effectively and comprehensively.”

But statements are unlikely to satisfy the Indian leadership. Delhi will now want concrete evidence that the Pakistan authorities are doing everything they can to stop the militants carrying out further operations.

To make matters worse for Islamabad, the same message is also being sent from Afghanistan, which has accused Pakistan of not doing enough to stop Taleban and al-Qaeda fighters crossing over the border to attack Afghan and Coalition forces.

Donald Rumsfeld, the US Secretary of State, today made an implicit criticism of Pakistan during a visit to Kabul, when he said that there was “no question” that militants were crossing the border and that greater effort had to be made to stop the infiltration.

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