The US government urged Pakistan on Friday to prevent displaced Haqqani militants from returning to their traditional sanctuary after a Pakistani military offensive near the Afghanistan border.

The Haqqani network, which mainly operates out of Pakistan's border areas, has been blamed for some of the deadliest and most sophisticated attacks on NATO and Afghan troops in Afghanistan.

“What we've asked for is that the Haqqanis, yes they've been displaced, yes they've been disrupted, but that they not be allowed to regroup and resettle back into those historical areas,” said Jeffrey Eggers from the White House's National Security Council, speaking at a security forum in Colorado.

That would break a long tradition of tolerating those who did not target the Pakistani state. No one from the Haqqani network has been reported killed, however, since the offensive began in June in the remote region of North Waziristan.

The United States has long pressed for Pakistani action against the Haqqanis. Islamabad has said it would target any militants, including the Haqqanis, as they proceed with the military operation.

Pakistan's envoy to Washington, Jalil Abbas Jilani, sitting alongside Eggers and others at the event, acknowledged that Haqqani fighters almost certainly fled the region ahead of the military operation because it was pre-announced.

But Jilani also urged more to be done across the border in Afghanistan to deal with any militants who may have fled there.

“We are having good cooperation but I think something more is required to be done in order to make sure that the successes ... are conclusive,” Jilani said.

Afghanistan's envoy to Washington, Eklil Hakimi, said his information suggested that Haqqani militants had safe passage inside Pakistan and were going elsewhere inside Pakistan.

John Allen, the retired four-star general who led US and NATO forces in Afghanistan, voiced skepticism about Islamabad's past willingness to go after the Haqqanis, even as he acknowledged the opportunity presented by the ongoing offensive.

“When I was commander there, the Haqqani killed or wounded over 500 of my troops. And the operations in Waziristan somehow missed them every time they conducted ops on the eastern side of the border,” Allen said at the event.

US lawmakers warn that Pakistan will have to crackdown on the Haqqanis or lose millions in US military aid.

“What matters now is how this continues and whether or not the Haqqanis are afforded a sanctuary to return to when the operation gets into its terminal phase,” said Eggers, the senior director for Afghanistan and Pakistan at the NSC.