WASHINGTON (Reuters) -- The CIA officer who led the first American unit into Afghanistan after the September 11, 2001 attacks said Wednesday his orders included an unusual assignment: Bring back Osama bin Laden's head on ice...

...A 32-year CIA veteran with extensive experience in South Asia and the Middle East, Schroen was charged with the primary task of building up Northern Alliance forces so they could join U.S. troops in the overthrow of the Taliban.

But in the days that followed the worst terror attack on U.S. soil, Schroen said his boss at the CIA also told him and his deputy in no uncertain terms to kill the al Qaeda leadership.

"What he said [was], 'I would like to see the head of bin Laden delivered back to me in a heavy cardboard box filled with dry ice, and I will take that down and show the president. And the rest of the lieutenants, you can put their heads on pikes'," Schroen told Reuters in an interview.

He was quoting Cofer Black, then the director of the CIA's counterterrorist center.

"I don't think he meant that in detail ... I think he meant to impress upon me and my deputy that this was very serious business and he wanted to get our adrenaline charged," Schroen added...

...Schroen recounts his post-September 11 Afghan experience in the book "First In: An Insider's Account of How the CIA Spearheaded the War on Terror in Afghanistan," which will be published next week...

..."Other than in paramilitary operations, I have never in 32 years heard of an order to kill anyone. And in fact up to that day, my orders and the orders the CIA was operating under were primarily to try and capture bin Laden alive," he said...