A soldier shares his post on a lawless border

Lt. Andrew Brundson with one of his men from the 172nd Infantry Brigade
CBS News

Pakistan said Tuesday that an American drone fired two missiles at a house near the Afghan border, killing three people. Just last week U.S. officials accused Pakistan of supporting terrorists who cross from Pakistan into Afghanistan to fight American troops.

One of the reasons U.S. troops are fighting in Afghanistan after nearly ten years is the lawless border with Pakistan.

CBS News correspondent Willem Marx visited the region, and reports that the enemy finds it easy to operate there.

Army Lieutenant Andrew Brundson, from Boulder, Colo., climbed up to visit his men at a tiny outpost overlooking the border that separates Afghanistan from Pakistan.

"I want to be here. I want to be on the edge of it. I want to be where the rubber meets the road. I want to be on the border," Brundson said.

Brundson's men, with the 172nd Infantry Brigade, are searching for an enemy they can rarely touch. The enemy uses Pakistan, just over the border, as a haven to recruit, rearm and regroup.

CBSNews.com special report: Afghanistan

"Often times, if a man slips across the border, though we could pursue him, though it's within our weapons and the capability of our men, it's not what we do because this is the border region. We try, as much as possible to stay on our side of it," Brundson said.

These American soldiers may be the only ones "staying on their side." The border is unmarked, mostly unguarded. The tribesmen on both sides are Pashtun - one culture, one language.

"For us it's a matter of finding a needle in a haystack, finding where they are coming in across the mountain range. We have to make sure that when we see them we can identify that they are indeed insurgents and not just a nomad goat-herder moving across the border," Brundson said.

Every few days, the militants fire rockets at the U.S. base. The Americans fire back. But most often the enemy escapes to safety in Pakistan. Lieutenant Brundson knows people back home debate this war, and he told us this.

"I'm glad people question it. I hope they continue to do so. I question it myself and when I question it I come to the conclusion that this is an important thing to be doing. This is an important place to be. This is something that is worthy of my efforts, this is worthy of the risks my men are taking," Brundson said.

There is risk taking we can't see from here, such as strikes by U.S. special forces and CIA drones. But in these vast mountains, with outposts few and far between, the enemy moves easily across a border only the Americans choose to recognize.