The rockets, launched from crude wooden tripods and set off by timers, exploded at 2 a.m. several hundred yards from U.S. soldiers in the tense town of Khost, Maj. Bryan Hilferty said.
Monday's incident was the latest in a series of attacks apparently aimed at troops based in Khost.
"They are generally set up the same way, they put them on a little tripod, you just build two sticks together, you put a rocket on there, you put a timer and the rocket goes off when the timer goes off," Hilferty told reporters at Bagram Air Base, the coalition's Afghan headquarters. "Obviously they are badly aimed but it's still trouble. If we rid the country of all these excess amounts of ammunition it'll be a much safer place."
Hilferty said two large operations aimed at hunting down elusive Taliban militia and the Islamic militant al Qaeda network in eastern and southeastern Afghanistan were continuing.
Neither operation had encountered any Taliban, the hardline movement ousted in December after a U.S. air campaign, or al Qaeda, blamed for the Sept. 11 attacks on the United States.
In southeast Afghanistan, British Lt. Col. Paul Harradine said a 1,000-strong force led by British Royal Marines had scaled two peaks soaring to more than 11,000 feet.
The Marines conducting "Operation Snipe" - part of Britain's biggest combat deployment since the 1991 Gulf War against Iraq - also came across a well-camouflaged, but uninhabited, settlement that appeared to have been recently built.
Harsh conditions have taken their toll on a handful of coalition troops, military officials said Sunday. Three British troops were evacuated Saturday to Bagram air base from a mountain in the southeast of the country, Harradine said. Two of the soldiers were suffering from altitude sickness and a third had dysentery.
The Marines prepared on Sunday to search some of their most hostile terrain so far: two soaring peaks where Taliban and al Qaeda fighters may be hiding.
In other developments: