United States has virtually defended Hamid Karzai for his 'threat' to send troops after Taliban militants inside Pakistan, saying the Afghan president had simply the security of his people in mind and the comment was not directed against Islamabad.

"I don't think Karzai's comment was a threat. He is dealing with a very difficult situation on his border and is interested in protecting his people from forces, who want to attack them," White House Deputy Press Secretary Tony Fratto said.

The United States wants the Asian neighbours to work together to root out terror groups along their border, the senior official said.

"We need them working together on where these militias are and whether it's Taliban or Al Qaeda [Images]. And they need to come to an agreement in ways to try to diminish the impact of those groups.

"But we need to see more cooperation between the two governments and to bring down the level of tension and understand -- or come  to an understanding that they can work together to stop these groups, because these groups are a threat to both countries and both governments," Fratto said.

Meanwhile, the State Department Deputy Spokesman Tom Casey has said that Washington has again impressed upon Islamabad to join in its war against terrorism.

"We've certainly raised our concerns with them regularly about the importance of being able to work with us to fight extremism in the FATA. Obviously, the parties that are currently in power in the Pakistani government have suffered directly at the hands of their own internal extremists, so they have, certainly, a desire to combat terrorism. And we intend to be able to work with both of them to try and achieve that objective," Casey said.