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SEOUL, July 27 (Reuters) - A South Korean woman held hostage by the Taliban pleaded for help and a speedy release of 21 people and herself in their first known contact with the outside since they were abducted last week outside of Kabul.

The weeping voice, which spoke in Korean and an Afghan dialect of Farsi in a telephone interview with CBS News, is believed to be that of Yoo Hyun-joo, a 32-year-old nurse who joined the group of church volunteers about two weeks ago.

"We are held here in very difficult conditions every day," Yoo spoke in Korean in a recording of the interview posted on CBS News Web site. "Please help us so that we can come out as soon as possible."

Yoo's brother said he could immediately recognise her voice, South Korea's Yonhap news agency said.

The hostages, including 18 women, were abducted from a bus in Ghazni province last week while on a volunteer mission sent by a church located outside Seoul.

A church pastor who was leading the group was found dead on Wednesday with bullet wounds after the Taliban accused the Afghan and South Korean governments of failing to act in good faith.

The Taliban has given the Afghan government a list of prisoners they wanted freed as part of an exchange, Ghazni's governor Mirajuddin Pathan said.

Yoo said she was being held with 17 other women and the men were being held separately. She was not aware of any men being killed, CBS News said in a report on its Web site.

"Please help so that each one of us can go back unharmed," Yoo said.

South Korea has sent a senior envoy to Afghanistan to step up efforts to free the hostages. Chief presidential national security adviser Baek Jong-chun is expected to arrive on Friday.

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