It seems that Osama bin Laden is the prime suspect in the bombings. He has been given asylum in Afghanistan, so maybe that is why it's being bombed.

I was surprised to find out that bin Laden and the USA were "allies" once.

Bin Laden came to prominence fighting alongside the U.S.-backed Afghan mujahedeen – holy warriors – in their war against Soviet troops in the 1980s. But former followers say he turned against the United States during the 1991 Gulf War, seething at the deployment of U.S. troops in Saudi Arabia during the Gulf War campaign to oust Iraq from Kuwait. He has repeatedly called on Muslims worldwide to join in a jihad, or holy war, against the United States.

From the San Diego Union-Tribune.