The U.S. must keep working to salvage its relationship with Pakistan in order to preserve security in the region and protect against potential proliferation of that country’s nuclear weapons, top Pentagon leaders said Thursday.

Amid escalating tensions with Islamabad, Capitol Hill lawmakers have complained that Pakistan is not doing its part to go after terrorists within its borders, and they have pressed for cuts in U.S. aid to the country.

But Thursday Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, warned that the U.S. cannot afford to let its relationship with a crucial nuclear-armed country deteriorate.

“Those things that I fear in the future,” Adm. Mullen told Pentagon reporters, are “the proliferation of that technology, and it’s the opportunity and the potential that it could fall into the hands of terrorists, many of whom are alive and well and seek that in that region.”

Anger and frustration with Islamabad has escalated in recent days amid reports that Pakistani intelligence officials arrested informants who helped the U.S. in its May 2 raid that killed Osama bin Laden.

Mullen, who has made repeated trips to Pakistan in an ambitious effort to build relations, said he has delivered no message to Islamabad warning that aid will be cut unless cooperation improves.

And Defence Secretary Robert Gates said that U.S. and Pakistan need one another, and that the lines of communication must stay open. Both he and Mullen repeated assertions that the bin Laden raid caused much consternation among the Pakistan leadership, and they must be given time to work through it.

Mr. Gates said Pakistan has 140,000 troops on the Afghan border and they have worked to go after insurgents in South Waziristan and the Swat Valley. Their presence alone, he said, creates uncertainty among terror groups who think the Pakistanis played a role in the bin Laden raid and are worried they may be betrayed next.

If the relationship with Pakistan crumbles or “were we to walk away, I think it’s a matter of time before the region is that much more dangerous and there would be a huge pull for us to have to return to protect our national interests,” Adm. Mullen added.

On a similar issue, Adm. Mullen said that aid to Yemen still is stalled, as the country wrestles with violent unrest and government upheaval. He said the aid program was interrupted by the chaos there, and once that ebbs the U.S. will consider what next steps to take.

Last year as officials worked to counter the growing terror threat in Yemen from al-Qaeda in the Arabian Peninsula, the U.S. approved more than $150 million in aid to Yemen. And there were suggestions that the total would grow to as much as $250 million this year.

But budget constraints trimmed the military assistance program, and the unrest in Yemen has further stymied plans to provide additional aid, including more helicopters, equipment and training.

In one other announcement, Mr. Gates said Adm. Jon Greenert will become the next Navy chief. Greenert is currently serving as the vice chief of naval operations.

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