“The secretary wanted to take advantage of the fact that Admiral Mullen would be in the region to reinforce our concern with the Pakistanis about the spike in violence in Afghanistan and to keep the pressure on in the tribal areas,” Geoff Morrell, the Pentagon press secretary, said in a telephone interview about Admiral Mullen’s Pakistan stopover.

Capt. John Kirby, a spokesman for Admiral Mullen, said it was apparent to the admiral that “the Pakistani leadership is aware of their challenges in the border region, as well as of U.S. military concerns there, and are working to address those challenges.”

Pakistan, for its part, has complained that American forces have repeatedly hit Pakistani territory, in particular on June 10, when United States air and artillery strikes killed 11 members of the Pakistani paramilitary force, the Frontier Corps, manning a border post.

General McKiernan did not comment on the June 10 attack since a three-party investigation into the border clash had not yet been concluded, but he was very clear that militants were using their sanctuary in Pakistan to fire across the border and that the NATO and American forces had the right to fire back. “We have the ability to protect ourselves,” he said.

“The point that I am trying to make is that the border security situation is not good, and that border runs for 2,500 kilometers,” or about 1,500 miles, he said.

While he expressed optimism that the American-led forces here would prevail and the insurgency would be defeated, “I look at this problem regionally, the viable outcome in Afghanistan to a large degree is dependent on some outcome in Pakistan with these tribal areas. That is a problem that is not getting better with time.”

The base that came under attack in Kunar Province on Sunday lies in one of the most inhospitable mountainous regions where American forces have frequently faced fierce battles with insurgents.