The Mumbai terror attacks jeopardised operations against the Taliban in the remote parts of Pakistan, according to the US defence chief.
The attacks were a tactical operation that had strategic effects, chairman of the US Joint Chiefs of Staff Admiral Mike Mullen told reporters on the flight home after a visit to Pakistan.
It placed progress against Taliban extremists using safe havens in Pakistan's remote areas in jeopardy, he said.
Before the attack in Mumbai, the Pakistani government began operations in Baijur on the border with Afghanistan, Mullen pointed out.
During his trip, Mullen met top military and intelligence officials in Pakistan including the chief of the Army Staff Gen Ashfaq Kayani, and director-general of Pakistan's Inter-Services Intelligence Lt Gen Ahmed Shuja Pasha and apparently discussed the Mumbai atatcks.
"It was a good, positive meeting, and it continues our relationship," Mullen said, according to a report on the US defence department website. "I'm not going to get into specifics of what we discussed, but I am encouraged."
Mullen and NATO International Security Assistance Force (ISAF) officials said that the Baijur operation was extremely helpful inside Afghanistan.
The Pakistani army operation, combined with coalition and Afghan military efforts, caused a noticeable drop in Taliban fighters and members of other terror groups trying to cross the border, he added.
But the small team of extremists that attacked Mumbai placed that progress in jeopardy.
US officials believe extremists from the terrorist group Lashkar-e-Taiba used the safe havens along Pakistan's border with Afghanistan, to finance, plan and train for the Nov 26 terror attack against India's financial capital Mumbai.
The near-term danger is that war might erupt, the report quoted officials as saying. "A second-order effect is that the dispute may cause Pakistan to concentrate on its border with Kashmir and lessen its commitment to solving the problem of safe havens in the west."
The long-term answer, Mullen was quoted as telling reporters, is a regional strategy that includes Pakistan, Afghanistan, India and other central Asian nations. The nations must improve relations between one another so attacks like the one in Mumbai don't escalate closer to conflict, he said.
Military-to-military contacts can help lessen tensions among the countries of the region and put in place a structure for working out problems, Mullen said.
Describing the relationship between the US and Pakistan as critical, Mullen said the NATO and Pakistani operations are coordinated, but aren't synchronised.