GHAZNI, Afghanistan - A purported Taliban spokesman said Monday that the militants will continue kidnapping foreigners in Afghanistan, as Afghan doctors dropped medicines for the ailing South Korean hostages held by the group since July 19.

Qari Yousef Ahmadi, who claims to speak for the Taliban, said that the lives of 21 South Korean hostages rest on the shoulders of Afghan President Hamid Karzai and President Bush, who are holding two days of talks at Camp David, Md.

"Karzai and Bush will have responsibility for whatever happens to the hostages," Ahmadi said.

Karzai said in an interview aired Sunday that the Afghan government is working to free the hostages, but he indicated it wouldn't give in to Taliban demands to release imprisoned militants in exchange for the Koreans' lives, in part fearing it would only encourage more kidnappings.

Ahmadi, however, said the Taliban will continue with its methods.

"Whether the Kabul administration will do the (prisoner) exchange or not, it will not have any effect on our side. The process of kidnapping (foreigners) will be ongoing," Ahmadi said.

Meanwhile, an Afghan doctor who heads a private clinic said he dropped off $2,000 worth of antibiotics, vitamins and first aid kits in rural Ghazni province Sunday intended for the Koreans, two of whom are said to be extremely ill. Dr. Mohammad Hashim Wahwaj said the Korean's Taliban captors told him they had picked up the medicines.

The Taliban have demanded that 23 militant prisoners being held by Afghanistan and at the US base at Bagram be freed for the Koreans, but the Afghan government has all but ruled that option out.

"We will not do anything that will encourage hostage taking, that will encourage terrorism. But we will do everything else to have them released," Karzai said the interview broadcast on CNN Sunday.

Twenty-three South Koreans from a church group were kidnapped by the Taliban July 19 while traveling from Kabul to Kandahar to work on medical and other aid projects. Two male hostages have been executed. Among the remaining 21 hostages, 16 are women.

If an agreement is not reached for in-person negotiations, then the Taliban will not be responsible for "anything bad" that happens to the hostages, Ahmadi said.

He also said that the militants and South Korean officials remain in contact over the phone, but have not yet agreed on a location where they can hold negotiations on the fate of the captives.

In Seoul, an official said Monday that South Korean diplomats had made contact with the captives. The official, who spoke on condition of anonymity because of the sensitivity of the issue, declined to give further details about the conversation with at least one of the captives, citing safety concerns.

About 150 demonstrators rallied at the US Embassy in Seoul, praying for the hostages' release and demanding US help.

In Afghanistan, foreign and Afghan troops thwarted a Taliban ambush at a checkpoint in the south and killed 13 suspected militants, a local official said.

Troops battled the militants for more than two hours on Sunday in Zabul's Shahjoy district after they tried to attack the checkpoint on the main road linking Kabul to the southern city of Kandahar, said Ali Kheil, the spokesman for Zabul's governor.

NATO and the US-led coalition did not immediately confirm the clash.

Kheil said authorities recovered 13 bodies, along with nine AK-47 assault rifles, rocket-propelled grenades and two heavy machine guns.

No Afghan or foreign troops were hurt, he said.