The real reason, why Americans are seething with anger against Pakistan, is that their efforts to divide a wedge between the Talibans are backfiring on them. The masters who are known for their divide and rule games, are hitting a wall when it comes to the leadership of Taliban, united under Mulla's leadership. 

It is a well known fact that Haqqani are invertible arm of Taliban network not of Pakistan or ISI. Americans are well aware of it, but they are frustrated from their failures and Taliban's refusal to accept the dictate. 

First the yanks tried to use their discredited media to spread the rumour of contacts with Taliban, but it was disclosed that USA were either duped by an impostor like the one in the past who took money of the Americans or it was hoax raised by the Yanks themselves. 

Anyhow, the problem for the Americans is they cannot negotiate with Taliban at the moment unless they meet the demand of withdrawal first. Americans desires to establish their foothold in Afghanistan on permanent basis and installing a puppet like Karzai every time during their presence in Afghanistan is not going to bear fruit. There are going to be no super bases from where smart armies with the help of helicopters and Fighter jets could operate. 

Hence the frustration and anger with Pakistan. After overture with Indians, the Yanks realised, it is a wrong strategy, bringing Indians in would be counter productive. Like I explain, stoppage of supplies not only NATO ones, but to civilian population, including fuel and food, would have catastrophic impact in Afghanistan. People will rise against whatever stooge Government is installed in Kabul by the Americans.