India demanded Pakistan take decisive action over deadly attacks in Mumbai it said were carried out by militants from its nuclear-armed rival, while the West urged cooperation to ease tension.
US Secretary of State Condoleezza Rice and Arab League Secretary-General Amr Moussa both were due in New Delhi, with the militant attacks that killed 183 people in India's financial capital threatening to reverse improving ties with Pakistan.
India's foreign ministry said on Monday it called in Pakistan's envoy to New Delhi and told him attackers, who investigators said had months of commando training in Pakistan, had come from there.
"It was conveyed to the Pakistan high commissioner that Pakistan's actions needed to match the sentiments expressed by its leadership that it wishes to have a qualitatively new relationship with India," a foreign ministry statement said.
Pakistan, in a report by its official Associated Press of Pakistan, said its high commissioner had gone to the Indian foreign ministry "as per routine" and had not been summoned for a meeting or been issued with any official demarche.
Investigators said the militants were trained by the Lashkar-e-Taiba group, blamed for a 2001 attack on India's parliament. That event nearly set off the fourth war between the two countries since Pakistan was carved from India in 1947.
The attacks have prompted the resignation of the interior minister and offers to step down from other top politicians from the ruling Congress party coalition.
Facing an election by May, analysts say Prime Minister Manmohan Singh must walk a delicate line not to upset regional stability but act forcefully enough to counter opposition accusations Congress is weak on security.
Many Indians have expressed anger at apparent intelligence lapses, including what a senior coast guard official said was a warning militants would attack Mumbai from the sea days before it happened, and a slow reaction by security forces to the rampage.
The attacks against Mumbai's two best-known luxury hotels and other landmarks in the city of 18 million are a major setback for improving ties between the nuclear-armed neighbours.
Ms Rice was due to visit India on Wednesday, underscoring the gravity with which Washington saw the regional implications. She met British Foreign Secretary David Miliband in London today.
"I don't want to jump to any conclusions myself on this, but I do think that this is a time for complete, absolute, total transparency and cooperation and that is what we expect (from Pakistan)," Ms Rice told reporters.
Officials in Islamabad have warned any escalation of tensions would force it to divert troops to the Indian border and away from a US-led anti-militant campaign on the Afghan frontier.
Mr Miliband, after meeting Ms Rice, said joint action would "make the difference between stability and instability".
The Arab League's Moussa was due in New Delhi tomorrow.
European Union foreign policy chief Javier Solana on Monday called foreign ministers from both countries and urged Pakistan to make good on its promise to cooperate in the investigation.
Solana's office said that in his call to Pakistan's Foreign Minister Shah Mehmood Qureshi, Solana had "encouraged the Pakistani government to pursue the fight against extremism and terrorism and to support the Indian authorities in the investigation on the terrorist attacks".
Pakistan has vowed to cooperate with India in investigating the militant assault, but on Monday rejected what it called unsubstantiated allegations of complicity in the attacks.
It also backtracked on a decision to send the chief of its main Inter-Services Intelligence (ISI) security agency.
A French judge, Marc Trevidic, who focuses on Islamist militants, downplayed any possible link between the attacks and the Pakistani leadership.
"The Pakistan intelligence services, ISI, can be infiltrated but also manipulated by Islamist groups," he said.
Reuters