MARGARET WARNER: And to Pakistan and its strained relationship with the United States, as Washington pursues the war in Afghanistan.
Militants struck twice more at NATO supply convoys in Pakistan today. In one attack, some two dozen fuel tankers were torched and a driver killed on the outskirts of Quetta.
HAMID SHAKIL, deputy inspector general, Quetta (through translator): This morning, armed people came in two cars and opened fire. Those under fire fled, and some of these armed men went to the tankers and torched them. These are all oil tankers.
MARGARET WARNER: The truck convoys haul supplies to U.S. and NATO troops in Afghanistan, but last week's Pakistani government decision to close a key border crossing has left hundreds of trucks stranded along the highways, sitting ducks in the backed-up traffic.
The current standoff was triggered when two NATO helicopters flew into Pakistani airspace to conduct a raid last Thursday. They fired at and killed two Pakistani border guards at an outpost in Upper Kurram tribal area 200 yards inside the border.
The killings enraged Pakistan's government, and, within hours, it blocked the crucial Torkham crossing over the Khyber Pass. Usually, NATO supplies land at the Port of Karachi and are trucked to Afghanistan along a northern route through Torkham or a southwestern route through Chaman. The Chaman crossing remains open.
The Pakistani Taliban has claimed responsibility for several of the attacks. On Monday, NATO Secretary-General Anders Rasmussen formally apologized to Pakistan's foreign minister in Brussels. He called the killings of the border guards unintentional.
Today, the U.S. ambassador to Pakistan, Anne Patterson, issued an apology as well. Also today, a joint Pakistani/NATO investigation concluded that the Pakistani border guards had fired shots to alert the helicopters of their presence, but the helicopter crews mistook them for insurgents.
NATO and U.S. officials have said they expect the border crossing to reopen shortly. And, on Tuesday, Pentagon spokesman Geoff Morrell played down any long-term fallout.
GEOFF MORRELL, Pentagon spokesperson: There are incidents which create misunderstandings. There are setbacks. But that doesn't mean the relationship, this crucial relationship to us, is in any way derailed.
MARGARET WARNER: But the dispute has underscored tensions with the U.S. over Pakistan's willingness to press the fight against al-Qaida and the Taliban.
The Wall Street Journal reported today on a new assessment sent to Congress by the Obama administration, among its conclusions, "The Pakistan military has continued to avoid military engagements that would put it in direct conflict with Afghan Taliban or al-Qaida forces."
The report also says that challenges facing Pakistan's civilian leadership "have the potential to impact the stability of the government," and it says the government's failure to respond adequately to the recent flood disaster has sent public confidence to new lows.
The White House report's findings echo doubts voiced by administration officials in a new book by Bob Woodward. At one point, he quotes President Obama as saying, "We need to make clear to people that the cancer is in Pakistan."
Last week, at a Washington forum, the U.S. special envoy to Pakistan and Afghanistan, Richard Holbrooke, underscored the challenge.
RICHARD HOLBROOKE, special U.S. representative For Afghanistan and Pakistan: The overall relationship with Pakistan is complicated, more complicated than any strategic relationship I have ever been involved in.
But, in the -- at the end of the day, success in Afghanistan, however you define success, is not achievable, unless Pakistan is part of the solution, not part of the problem.
MARGARET WARNER: To shore up Pakistan, Congress last year approved a giant package of non-military aid: $7.5 billion over five years.
The U.S. has sent additional funds to help deal with the floods, more than $360 million so far.