The body of a second South Korean hostage shot dead by Taliban militants in Afghanistan is expected to arrive home on Thursday, while lawmakers left for the United States to persuade Washington to help end the standoff.

The remaining 21 South Korean hostages who have been held for two weeks are still alive, the Taliban said on Wednesday, while the army warned villagers to evacuate areas near where the insurgents are thought to be holding them.

The Taliban have shot dead two male hostages and threatened to kill more if their demands to trade the Koreans for jailed insurgents are not met.

The body Shim Sung-min, 29, a volunteer for charity groups, will arrive by air transport. His family said it would hold a funeral and then donate his remains for medical research.

Eight lawmakers hope to speak to US and UN officials "to appeal for the quick and safe return of our people in Afghanistan", they said in a statement.

Of the 21 hostages, 18 are women.

The South Korean government is under intense pressure to bring the captives home but concedes it has few cards to play. The government has called for "flexibility", a comment analysts say is directed at the United States to sway the Afghan government to strike a deal with the kidnappers.

The United States has said it does not make concessions to terrorists. But lawmakers are hoping Washington might make an exception to help bail out an ally which has sent troops to Afghanistan and Iraq.

South Korea's two largest conservative dailies said visits of this sort might stir anti-U.S. sentiment if the ordeal deteriorates even further and could hurt negotiations on freeing the hostages.

"Anti-American sentiments by some elements are only helping the Taliban and justifying their atrocities," the Chosun Ilbo, the country's largest newspaper, said in Thursday's editorial.

The Afghan government has refused to give in to demands to free Taliban prisoners, saying that would only encourage further abductions.

The 23 South Koreans were sent by a Christian church in suburban Seoul to do relief work in Afghanistan, even though their government warned them not to go because of safety concerns.

They were snatched from a bus on the main road south from the capital Kabul travelling through Ghazni province.

The first victim was the leader of the group, Bae Hyung-kyu, a pastor who was shot dead last week on the day he turned 42.