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“The war against terrorism must unite us and not oppose us,” Mr. Zardari said, noting that he had not canceled his visit to London “in spite of this serious breach” by the British prime minister.

“The relations between our two countries are old and strong enough for that,” he said.

But Mr. Cameron has shown no sign of backing down.

“I gave a pretty clear and frank answer to a clear and frank question,” the British prime minister told BBC radio on the eve of Mr. Zardari’s visit.

“I don’t regret that at all,” he said. “We have to work with them to close down the terror networks that are in Pakistan that … have threatened innocent people all over the world.”