(Adds church service)

By Jack Kim

ANYANG, South Korea, Sept 2 (Reuters) - Nineteen South Korean Christian volunteers held hostage by the Taliban in Afghanistan for six weeks returned home to an uncomfortable welcome on Sunday, thanking their government for saving them from death.

A senior Taliban leader told Reuters that Seoul had paid $20 million for their release, but the South Korean government denies paying any ransom -- although has been criticised internationally for striking a deal through direct negotiations.

"We went to spread God's love and carry out his wishes," freed hostage Lyu Kyung-sik said after arriving. "All of us returned from being on verge of death and have been given our lives back."

The hostages -- heads bowed, looking sombre and some fighting back tears -- stood behind Lyu as he made a brief statement at Incheon airport outside Seoul. He stood between framed pictures of the two hostages shot dead by the Taliban.

"All of us owe a big debt to the country and the South Korean people," said Lyu. "When thinking about the trouble we have caused them, it is proper for us to bow deeply and ask for your forgiveness."

The six-week standoff gripped the country, leading thousands to join candlelight vigils.

But many criticised the suburban Seoul Saemmul Church that dispatched the group as having a naive world view and for putting their government in a bind.

Web sites of the country's main Protestant groups and largest Internet portals have been flooded with messages saying the group and church were to blame for ignoring government warnings and for making an ill-advised mission to an obvious danger spot.

RANSOM AND MISSIONARIES

The hostages were taken to a hospital in Anyang, south of Seoul, where many collapsed into the arms of waiting relatives, who cheered when the group entered a reception room. A few of the group, overcome by emotion, had to be carried out of the room.

The former hostages, mostly women, were then admitted for medical checks and kept away from the media.

Seo Jeung-bae was reunited with a son and daughter. "I was given back the two children I had lost. By holding them in my arms, I now know it's real," the smiling father said.

About 1,300 crammed Saemmul Church for services on Sunday with a pastor saying it was not right for the government to seek compensation from it for costs incurred in securing the release.

"Saemmul Church is at the centre of a war against our will," pastor Park Eun-jo said in a message to parishioners about the criticism of its Afghan mission.

The South Korean government said it had agreed to pull out a small contingent of military engineers and medical staff and to end South Korean missionary work in Afghanistan in return for the release of the hostages.

It said there were no other conditions to the deal, although the Taliban had demanded swapping the Koreans for its prisoners.

South Korea had already planned to pull all its non-combat troops out before the hostage ordeal.

The number of South Korea Christian missionaries working abroad is second only to those from the United States.

Often, dozens or even hundreds of Korean evangelicals can be found abroad in a single small city fighting one another for exposure.

Taliban insurgents kidnapped 23 South Koreans in mid-July. They killed two male hostages as initial negotiations stumbled and last month released two women captives.

They have spoken of living in constant fear, split up into small groups and shuttled around the Afghan countryside to avoid detection.

South Korea is the second largest source of Christian missionaries, after the United States, with an estimated 17,000 abroad. For many Korean churches, the number of missionaries they send abroad is a reflection of the strength of their congregation.

Some church leaders said they would rethink their overseas missions but a leading group said the Afghan ordeal had only strengthened its resolve to send more missionaries overseas, even if it meant taking over negotiating hostage releases from the government. (With additional reporting by Lee Jin-joo, Cheon Jong-woo and Jon Herskovitz) ((Writing by Jon Herskovitz, Reuters Messaging: jon.herskovitz.reuters.com@reuters.net; +822 3704 5510))

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