David Cameron has insisted he had a duty to speak "clearly and plainly" about the threat of terrorism after claiming Pakistan must do more to tackle the issue.
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 on Wednesday. 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".
The high commissioner said: "He is new in government, maybe he will learn soon and he will know how to handle things. 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.