21 Afghans killed by rebels on Wednesday. President Karzai warns of further attacks

Fighting erupted across Afghanistan ahead of a visit Wednesday by U.S. Secretary of State Condoleezza Rice, with 10 suspected rebels, six police and five medical workers killed and rockets slamming into the capital. President Hamid Karzai warned that his nation could fall back into the hands of terrorists if its booming heroin trade.

Karzai's comments at a press conference with Rice came as his U.S.-backed government is struggling to strengthen a fragile democracy while dealing with a rebellion that has left about 1,400 dead in the past half-year.

The U.S. and other countries have pumped hundreds of millions of dollars into counter-narcotics programs, but it's had little impact, sparking warnings this nation is becoming a "narco-state" four years after a U.S.-led invasion ended its role as a haven for al-Qaida.

Karzai's comments were the first time he has directly linked the drugs trade with the rebellion. Washington earlier this year criticized the president for not being tough enough on narcotics and U.S. officials have said they suspect the insurgency is being partially funded by drug money.

In the latest violence, U.S. warplanes killed 10 suspected Taliban rebels in an attack on their mountain hideout in Uruzgan province, which has long been a hotbed of militant activity, local Gov. Jan Mohammed Khan said.

The killing of the five medical workers occurred Wednesday near the former Taliban stronghold of Kandahar city, said doctor Abdul Qadir, director of U.N. and U.S.-sponsored Afghan Help Development Services, a local aid group that employed the five. A.M.