India on Monday formally accused "elements" in Pakistan of being behind the devastating Islamic militant attacks in Mumbai and demanded that Islamabad take "strong action".
The move came after Indian officials said investigations had shown that all the attackers involved in the 60-hour-long assault, which left at least 172 dead and close to 300 wounded, were Pakistani nationals.
The attacks were also described as a "major setback" for the peace process between the nuclear-armed neighbours.
"The High Commissioner of Pakistan was called to the Ministry of External Affairs this evening. He was informed that the recent terrorist attack on Mumbai was carried out by elements from Pakistan," a statement said.
In New Delhi's first formal complaint to Islamabad, India said it "expects that strong action would be taken against those elements, whosoever they may be, responsible for this outrage".
A Jewish centre was among the targets and eyewitnesses said some attackers singled out Britons and Americans in two luxury hotels. Civilians were also gunned down in a railway station, hospital and a cafe.
"What has happened is a grave setback to the process of normalisation of relations and the confidence-building measures," Minister of State for External Affairs Anand Sharma told AFP.
Officials said they are convinced the Pakistan-based militant group Lashkar-e-Taiba, possible with assistance from sections within Pakistan's powerful spy service, staged the operation.
But Pakistan's government has denied it was in any way linked to the operation by the well-trained and well-financed attackers. Pakistan President Asif Ali Zardari has urged India not to "over-react".
India and Pakistan have fought three wars and were on the brink of a fourth over a 2001 militant assault on the Indian parliament.
India's ruling Congress party said any response would be "carefully considered" but made it clear that a line had been crossed.
"We have been confronted by a rising tide of terrorism for some time but the attack in Mumbai was qualitatively different and calls for immediate and stern action," Congress party spokeswoman Jayanti Natarajan told reporters.
US Secretary of State Condoleezza Rice, who is due to visit India on Wednesday, said it was crucial that Pakistan exhibit "complete, absolute, total transparency and cooperation" with the Indian investigation into the attacks.
"What we are emphasising to the Pakistani government is the need to follow the evidence wherever it leads and to do so in the most committed and firmest possible way," she told reporters accompanying her on a trip to Europe.
White House spokeswoman Dana Perino also said she had "heard nothing that says that the Pakistani government was involved," adding that US President George W. Bush was briefed in the White House situation room on the attacks.
US president-elect Barack Obama, for his part, vowed his administration was "absolutely committed to eliminating the threat of terrorism" and said the United States stood with India in the wake of the attacks.
Pakistan has repeatedly underlined that it is fighting its own battle against Islamist insurgents, who have taken their bloody campaign to the heart of the Pakistan capital and stressed the two nations have a common enemy.
Lashkar, which has been battling Indian troops in Kashmir, was banned by Pakistan in 2002.
|Map locating the attacks in Mumbai.|
Public outrage in India was fuelled Monday by fresh reports that clear warnings of a coming assault were ignored.
The Hindustan Times said a captured Lashkar operative had told his Indian interrogators back in February that the militant group was planning an attack on Mumbai's five-star hotels.
Tension between India and Pakistan date to the post-independence partition of India in 1947 that created the Islamic state of Pakistan and led to horrific bloodletting between Muslims and Hindus.
India has also had its share of homegrown unrest, from Muslims to Maoists to Hindu extremists, and Indian officials have repeatedly declined to blame Pakistan directly for the Mumbai attacks.