Jolted by video footage showing one of their countrymen being held in Iraq by kidnappers threatening to behead him, hundreds of South Koreans joined candlelight vigils and prayer groups Monday while the government scrambled to negotiate the hostage's release.

In the video, first broadcast Sunday by the Arabic satellite TV network al-Jazeera and rerun countless times here Monday, Kim Sun Il, 33, screamed for his life while his hooded, armed captors demanded that South Korea quit the international military coalition in Iraq. The video was released three days after the government had finalized plans to begin deploying its main contingent of 3,000 troops there this summer.

The kidnappers gave South Korea 24 hours from sunset Sunday to agree; otherwise, they said they would "send to you the head of this Korean."

After an urgent cabinet meeting, South Korean leaders rejected the demand and dispatched an emergency diplomatic mission to Jordan in an attempt to win Kim's release.

[By Tuesday morning, after the 24-hour deadline had passed, South Korean Foreign Ministry spokesman Shin Bong Kil said the government continued attempts to secure Kim's release but could not confirm whether he remained alive.]

A banner in the background of the video named Kim's abductors as members of Jamaat al-Tawhid and Jihad. The group is associated with Abu Musab Zarqawi, a Jordanian accused of having links to al Qaeda and blamed by U.S. officials for several recent kidnappings and car bombings in Iraq.

U.S. officials pledged to assist in the search for Kim, promising to use military and intelligence resources to help with any rescue effort. But they acknowledged that little progress had been made.

"We're developing that intelligence about where he was captured, under what circumstances he was captured, but I'm just not sure that we have built that body of intelligence yet," said Brig. Gen. Mark Kimmitt, the chief U.S. military spokesman in Iraq.

Kim was working as a translator for a South Korean contractor supplying goods to the U.S. military and had hoped to become a Christian missionary in the Middle East. He was kidnapped Thursday in Fallujah, 35 miles west of Baghdad, South Korean officials said.

Kim Chun Ho, head of Gana General Trading Co., which employed the abducted translator, told South Korea's semi-official Yonhap news agency from Mosul that "several other third-nationality employees" from the U.S. firm KBR, an affiliate of Halliburton Co., had been traveling in the same convoy as Kim Sun Il and were also taken hostage. The report could not be immediately verified.

Kim was kidnapped one day before South Korea outlined a much delayed schedule to begin sending 3,000 troops to Iraq starting in August. The deployment would make South Korea, which already has 660 non-combat troops in Iraq, the third-largest contributor to forces there, after the United States and Britain.

A majority of South Koreans are against sending the troops, surveys indicate, and the kidnapping led some opponents to demand that the government backtrack.

"Kim is an innocent citizen, and he should not be sacrificed in what is essentially an unjustified invasion," Kim Ki Sik, the head of a citizens' group opposed to the war, said during a demonstration with several dozen protesters Monday in downtown Seoul. "We oppose this war and we oppose the Korean government's decision to send troops despite the fact that the people are against it."

South Korean leaders have called the deployment vital to shoring up their country's alliance with the United States. Ties between the two allies have wavered in recent years, particularly in the last few months, as President Roh Moo Hyun has sought a closer relationship with North Korea even as the United States has tried to isolate the Pyongyang government over its nuclear weapons programs.

Vice Foreign Minister Choi Young Jin told reporters that South Korea's dispatch plan had "not changed," and Roh sought to emphasize South Korea's benevolent intentions.

"We need to make efforts to explain that our troops will focus on reconstruction efforts without conducting hostile activities against Iraqi people," Roh said in a statement in which he described the kidnapping as a "very sad incident."

"The government should handle the case in a calm manner and use all available diplomatic resources to rescue him unharmed," he said.

The circumstances surrounding Kim's capture remained sketchy, but Kim Chun Ho told Yonhap that the translator was taken hostage while returning from a delivery to a U.S. military camp 120 miles west of Baghdad with an Iraqi employee and other foreigners of undisclosed nationality working for KBR.

Kim's sister, Kim Jung Sook, 34, said in a telephone interview that her brother had been in Iraq for eight months on a one-year contract, and planned to return to South Korea in July for their father's 70th birthday.

She described her brother as a devout Christian who had earned degrees in Arabic, English and theology in the hopes of one day doing missionary work. She said Kim had accepted the translating job to earn money and continue his studies.

"He learned Arabic because he wanted to be a pastor or a missionary working in the Middle East," Kim Jung Sook said.

Kim's sister said she was putting her faith in the government to do what was right. "Just because of one person, we cannot just flip-flop our national policy," Kim said from her family home in Pusan, South Korea's second-largest city.

Kim's mother, Shin Young Ja, however, told local television reporters that while she once believed in the Iraqi mission, she now wanted the government to rethink the deployment for her son's sake.

Correspondent Scott Wilson in Baghdad contributed to this report.

Students carry posters of Kim Sun Il, who was kidnapped in Iraq on Thursday.