The Prime Minister ignored calls from Pakistan's high commissioner to London for him to "make amends" and repeated that Islamabad must "crack down" on terrorist groups.
But he stopped short of his provocative claim that Pakistan must not "export terror to the world" or be allowed to "look both ways" on the issue.
Apparently signalling a new era of straight-talking diplomacy, Mr Cameron said: "I believe in speaking clearly and plainly about these matters and we have seen not just the threat of terrorism but the reality of terrorism in the enormous losses that we saw on the streets of Mumbai, that we have seen on the streets of London, and that we see week after week in Afghanistan.
"It is not acceptable, as I have said, for there to be within Pakistan the existence of terror groups that cause terrorism both within Pakistan and also outside Pakistan, in Afghanistan, in India and elsewhere in our world.
"What we will continue to do is work with the Pakistan government to do everything that we can to encourage them to crack down and to take on these groups that have caused so much pain and so much suffering."
But his latest comments, at a joint press conference with Indian Prime Minister Manmohan Singh at the end of a visit to New Delhi, were not as strong as those he made off-the-cuff yesterday.
They caused Pakistan's high commissioner in London, Wajid Shamsul Hasan, to say that people in his country were "really hurt".
He also suggested that the Prime Minister had made a mistake because he was inexperienced.
Speaking to the BBC, Mr Hasan said he hoped Mr Cameron's comments were a "slip of the tongue" and "not a meant slight by him".
"He is new in government, maybe he will learn soon and he will know how to handle things," said the high commissioner.
"I hope he will make amends and he will pacify the people of Pakistan as well as the government of Pakistan because it has been taken here very adversely, people are really hurt."
Mr Cameron denied that he had damaged relations with Pakistan, a crucial ally for the Nato-led mission in neighbouring Afghanistan. Foreign Secretary William Hague insisted the Prime Minister was "a great diplomat... a natural".
But the PM faces a potentially difficult meeting with Pakistan's president, Asif Ali Zardari, when he visits his country retreat of Chequers next week.
He stressed that the focus of the visit to India was on deepening trade relations and thereby creating jobs back home.
After talks with Dr Singh, Mr Cameron said his two-day visit had seen "tremendous progress" in building the "very special relationship" between the UK and India.
Mr Cameron said: "I believe that the last two days have well and truly put in place the basis for an enhanced and enduring partnership between the UK and India.
"What was already a good relationship, I believe, can go so much further."
Dr Singh appeared to have responded to Mr Cameron's efforts, which included bringing with him a 67-strong delegation of ministers, businessmen and sports stars.
He praised Mr Cameron for showing "the finest qualities of leadership" and said they shared "the same vision for a renewed and enhanced partnership between our two countries".
Britain and India were "natural partners to shape a better world", the Indian premier said.
The two countries would intensify cooperation in the areas of counter-terrorism, education, research and cultural exchange.
They had agreed to work together on doubling trade within five years, as well as setting up an India-UK CEOs' Forum and India-UK Infrastructure Group to promote business links, the Indian premier added.
Asked about the remarks made by Mr Cameron on Pakistan, Dr Singh said: "I believe that after 9/11 the world community has recognised that terrorism constitutes a very important threat to all civilised societies in the world.
"Further, there is complete agreement that no cause is good enough to justify resort to terrorism.
"I certainly hope that the government of Pakistan would honour its commitments given to us on many occasions, that Pakistan territory will not be allowed to be used for acts of terrorism directed against India.
"We believe Pakistan should be as serious in paying attention to terror on the western borders of Pakistan as on the eastern borders.
"I hope that the world community will use its good offices to promote this cause."
