Cameron said he had given a "pretty clear and frank answer" to a straight question while visiting India last week. "I don't regret that at all," he told BBC radio.
Pakistani President Asif Ali Zardari is due to arrive in Britain for a five-day visit later Tuesday. He is due for talks with Cameron on Friday.
"The key thing is to build on the relationships we have," Cameron said. "It's a relationship that I'm convinced can survive speaking frankly about our problems."
He said there were terrorist groups in Pakistan that "threaten innocent people the world over", adding that Islamabad had done "extraordinary things to try and close them down", but needed to do more.
Cameron's original comments on Pakistan and terrorism were made Wednesday in Bangalore.
"We cannot tolerate in any sense the idea that this country (Pakistan) is allowed to look both ways and is able, in any way, to promote the export of terror, whether to India or to Afghanistan or anywhere else in the world," he said.
Pakistani British lawmakers slam Zardari's visit
British lawmakers of Pakistani origin hit out at President Zardari the same day, saying he should be back home sorting out the flooding disaster rather than launching his son's career.
"I'm not going to meet with the president because I believe that a head of state needs to be in his country of origin when there's a state of emergency," Lord Nazir Ahmed told AFP.
"For him to spend tens of thousands of pounds on the launch of his son's political career at a time when his country needs him shows that he's out of touch and his advisors are ill-informed,” he said.
"Quite frankly, staying in five-star hotels with his huge entourage, tens of big cars that have been hired just to give him this protocol in London, it's quite outrageous."
Ahmed, from the opposition Labour Party, has pulled out of Thursday's lunch event at a London hotel.
"I would rather the money should go to the flood victims than wasting money on a five-star lunch. I could have easily met him at the high commission for a cup of tea," the Pakistan-born peer said.
Fellow Labour lawmaker Khalid Mahmood has also turned down his invite, insisting Zardari should be in Pakistan rather than visiting Britain for political reasons.
"The issue is the huge environmental catastrophe that's going on, a lot of people are dying there," he said.
"No matter what he can do or can't do, he should be there to try to support the people, not swanning around in the UK and France."
A spokesman for Baroness Sayeeda Warsi, Britain's first female Muslim Cabinet minister, told AFP she will be attending the meeting.
Qassim Afzal, a senior Lib Dem politician of Pakistan origin, said he would attend the meeting, even if "British Pakistanis themselves feel that at this moment in time he should have stayed in Pakistan."
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