NEW DELHI (Agencies) - In the wake of Mumbai terror strikes, India's External Affairs Ministry on Monday summoned Pakistan's High Commissioner Shahid Malik to lodge protest over Pakistan's failure to curb terrorism emanating from its soil and also formally accused "elements" in Pakistan of being behind the militant attacks and demanded that Islamabad take "strong action". An Indian television channel reported that New Delhi also presented a list of 20 suspected persons, including Hafiz Muhammad Saeed, Dawood Ibrahim and Masood Azhar, to the Pakistani envoy and demanded that they be handed over to India. "The High Commissioner of Pakistan was called to the Ministry of External Affairs this (Monday) 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". India's Foreign Ministry has said investigations have shown that all the militants involved in the Mumbai attacks were Pakistani nationals. India handed over the written protest just hours after New Delhi warned the carnage in Mumbai was a major setback for the peace process launched by the South Asian neighbours in 2004. Our Staff Reporter from Islamabad adds: Pakistani officials denied that the Pakistan's Ambassador to India was summoned by the Indian Ministry of External Affairs to lodge a formal protest over Mumbai attacks. Pakistani Foreign Office said all the modes of communications between India and Pakistan were open and there was a procedure in this connection which was followed everywhere. He said Pak High Commissioner was not summoned. Indian High Commissioner to Pakistan Satya Pal also visited Pakistani Foreign Office Monday along with Deputy High Commissioner of India and discussed the Mumbai attacks with Foreign Secretary Salman Bashir, said an official here requesting anonymity. He said that the visit of Indian High Commissioner to Foreign Office was a routine matter and his meeting with Foreign Secretary was preplanned, as was the case with the visit of Pakistani Ambassador Shahid Malik to the Indian Foreign Ministry. APP adds: Diplomatic channels between Pakistan and India are fully operational, FO spokesman Muhammad Sadiq said in response to a question regarding diplomatic contacts between the two countries. For example, he said the Pakistani High Commissioner in New Delhi was received by the Special Secretary at the External Affairs Ministry at 6:30 pm (New Delhi time) while the Indian High Commissioner was received by the Foreign Secretary at 7:00pm (Islamabad time) on Monday. During the meeting with Indian High Commissioner, the Spokesman said, the Foreign Secretary "condemned the barbaric attacks, condoled with the families of the victims and people of India, and reiterated the assurances of our cooperation." The Foreign Secretary refuted the unsubstantiated allegations by the Indian media of Pakistan's complicity in the Mumbai incident, the Spokesman added. Meanwhile, Indian Minister of State for External Affairs Anand Sharma warned that the Mumbai attacks were a major setback to relations with Pakistan and promised a "stern" response. "What has happened is a grave setback to the process of normalisation of relations and the confidence-building measures," Sharma told AFP. He said the gunmen were "all from Pakistan" and that Islamabad had failed to deliver on its promise to prevent Pakistani soil being used for attacks on India. India's Deputy Home Minister also said that the Mumbai attackers were all from Pakistan. "We are not saying that it is sponsored by the Pakistan government," India's Deputy Home Minister Shakeel Ahmad told the BBC, adding that Pakistani soil was nevertheless being used for "anti-India" activities. "The terrorists who have been killed in these encounters in Mumbai in the last few days were of Pakistani origin," Ahmad said, as well as the lone gunman arrested after the stunning coordinated attacks in India's financial capital. 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. Maharashtra Chief Minister Vilasrao Deshmukh said Monday he had offered to resign amid widespread public anger over perceived intelligence and security failings that contributed to the bloodshed. His deputy, RR Patil, had stepped down earlier in the day. Meanwhile, investigations into the attacks shifted further towards the suspected role of Lashkar-e-Taiba Monday, threatening a fragile peace process between New Delhi and Islamabad. "There is a view in the government that India should suspend the peace process to show that it is not going to take lightly the deadly carnage in Mumbai," official sources told the official Press Trust of India (PTI). The government, "including Prime Minister Manmohan Singh, is very upset as it feels that Pakistan has not kept its promise made at the highest level to end terrorism directed at India," PTI said. Meanwhile, Vilasrao Deshmukh, who offered to resign as Chief Minister of Maharashtra, said that initial investigation revealed that Pakistan was not involved in Mumbai's terrorist attacks. Talking to mediamen after provincial cabinet meeting in Mumbai, he said terrorists had not made anybody hostage in the hotels. The Maharashtra CM said if terrorists had made any inmate hostage, they would have set conditions for their release, Pakistan state TV reported. Meanwhile, newly-appointed Indian Home Minister P Chidambaram assured the people that the government would respond with determination and resolve to the grave threat of terrorism posed before the Indian nation and soul of the country, reports Indian news channel Doordarshan. In a brief statement to media after taking charge of the Home Ministry, Chidambaram said he recognised the sense of anguish and deep shock among the people of India and the government would respond to the grave "threat posed to the very idea of India, soul of India, an India we know and love and which is secular, plural, tolerant and (has) open society." Meanwhile, the all-party conference convened by Prime Minister Manmohan Singh on Sunday night unanimously agreed on a slew of measures to fight terror but failed to achieve a broad political consensus across the political spectrum, reports CNN-IBN television channel. The Indian government came under severe attack at the meeting when Congress ally Samajwadi party accused it of being weak and demanded action within 15 days. Indian Prime Minister Manmohan Singh gave his assurance to senior politicians attending this meeting here that his government would act and come up with a blueprint to combat terror. The Bharatiya Janata Party and J Jayalalitha's AIADMK demanded stringent laws and protested the repeal of Prevention of Terrorism Act (POTA). The BJP came down harshly on the failure of the government to contain terrorism. "We have asked for an immediate session of Parliament so that everything can be discussed there," BJP's CM candidate V K Malhotra told CNN-IBN. But it was Samajwadi Party chief, Mulayam Singh Yadav's remarks which came as a surprise. He argued that the faith in this government has been shaken after the Mumbai siege and the government needed to come up with a concrete plan within the fortnight. While a section of the Left Front demanded the removal of the National Security Advisor, M K Narayanan, even the Telegu Desam was scathing in its attack on the government's mishandling of terror. Telugu Desam party leader Yerran Naidu said the Prime Minister promised the parties that the government would enact stringent laws to tackle terror and strength the national Security Guards(NSG). The Prime Minister has given an assurance that he would get back to the parties in a fortnight, Naidu said. CPI(M) leader Prakash Karat said India should go to the UN Security Council on the issue of terrorism while Jayalalaithaa's AIADMK demanded revival of the tough POTA. CPI leader A B Bardhan warned the government against any military misadventure against Pakistan.