By Jonathan Marcus
BBC diplomatic correspondent
Protesters in Mumbai have chanted anti-Pakistan slogans
India seems to be carefully building a public case to show that the perpetrators of the attacks in Mumbai were trained in and sent on their mission from Pakistan.
Indeed, as far as India is concerned the ball is now firmly in Pakistan's court.
India asserts that Pakistan harbours groups that have carried out attacks against Indian targets on a number of occasions seemingly with impunity: the time has come, they believe, for the authorities in Islamabad to act against them.
There are growing fears that if Pakistan's government does not act, then some kind of Indian military action - possibly against militant training camps - may follow.
That is why US Secretary of State Condoleezza Rice went hotfoot to the region, cutting short a trip to Europe.
Risk of stand-off
Her clear purpose in coming to India was to show solidarity and to urge restraint.
But in a message clearly aimed at Pakistan she said that there was "urgency in bringing the perpetrators to justice" and that there was urgency too, to "disrupt and prevent further attacks".
The stakes are high. The Indian authorities are under strong public pressure to act after the terrible events in Mumbai.
By acceding to Indian pressure Pakistan might risk deeper civil strife at home
Pakistan's government - ostensibly one that hoped to chart a new course with its more powerful neighbour - is between a rock and a hard place.
Pressure is mounting from India for Pakistan to take action itself against the militants that may have been involved in the Mumbai attacks.
But the authorities in Islamabad may doubt the capacity of their own security forces to carry out such orders.
And by giving in to Indian pressure Pakistan might risk deeper civil strife at home.
Overt Indian military action might provoke a new stand-off between these two nuclear-armed countries.
The head of Pakistan's army, Gen Ashfaq Kayani, has sought to calm tensions: a statement issued after a meeting of senior commanders said they "hoped that peace and stability in the region would be maintained".
Ms Rice has said that she has found Pakistan's leaders to be "focused and committed" to helping India probe the attacks.
Condoleezza Rice has been trying to defuse tensions
India and Pakistan have fought three wars since 1947 and came very close to a renewed conflict after extremists attacked the Indian parliament in December 2001.
Indian military strikes would do nothing for Pakistan's stability, which remains an ever-shakier cornerstone of US and Western efforts to win the war in Afghanistan.
Barack Obama's administration will be watching developments closely.
The US president-elect has taken the view that all of the region's problems are inextricably bound up.
Pakistan cannot devote sufficient attention to dealing with domestic extremists along with Taleban and al-Qaeda sympathisers in its border region with Afghanistan unless the historic tensions with India are resolved.
This, US experts believe, means that the long-standing Kashmir problem will have to be tackled.
This comprehensive approach, it must be said, is not necessarily shared by the Indians.
But the horrors in Mumbai will only have confirmed the incoming Obama administration in their belief that this is the best way to move ahead.