The thump of a Buddhist monk's drum echoed through the neon-laced avenues of central Seoul. The sound was a solemn soundtrack for hundreds of South Koreans offering sticks of traditional incense in protest and remembrance on Wednesday, a day after the beheading in Iraq of their countryman, Kim Sun Il.

But in a nation where most citizens are opposed to the government's involvement in Iraq, the anger was directed not only at the extremists who decapitated Kim, 33, a translator known mostly for his religious devotion and gentle manners. It also was focused on the long-standing U.S.-South Korean alliance, which many see at the core of the tragedy and which is polarizing this country of 48 million in a manner unseen since the Korean War.

Kim's captors executed him on Tuesday after the South Korean government rejected their demands to pull out of the U.S.-led effort in Iraq. The reaction to his death appears to further delineate a national schism between those in favor and those against the half-century-old friendship with the United States, while generating a fresh wave of anti-American sentiment.

"This was not our war. We are there out of responsibility to our alliance with the United States," said Park Eun Joo, 28, a human rights activist, who was weeping by an incense pyre and holding a sign demanding "South Korean Troops Out of Iraq."

"But the truth is the Iraqi people don't want us there -- it is that simple," she said. "Yes, I blame the militants for what happened. But I also blame George Bush for pressuring South Koreans to go against our will. Now, an innocent South Korean is dead."

Nearby on the sidewalk, however, Kim Bit Nari, 18, shouted at the protesters. "Sometimes a Korean has to die for his country!" she said. A music major at a local university, Kim expressed strong support for good relations with the United States: "Look, South Korea is a weak country; we just can't protect ourselves alone in this world."

South Korea dispatched 660 medical and engineering troops to Iraq last year, acting on a U.S. request. After months of delay, the Seoul government last week firmed up plans to send its main contingent of 3,000 troops -- a mobilization that will make the South Koreans the largest foreign force in Iraq after the United States and Britain.

Unlike other allies involved in Iraq, South Korea's leaders have not focused on the war in moral terms. Rather, the nation's participation has been pitched to a largely skeptical populace as a necessary evil. If South Korea sends troops to Iraq, the government has argued, the Bush administration is likely to moderate its position in dealing with North Korea. While the United States has taken a hard line on North Korea's illicit nuclear program, South Korean officials are aiming at rapprochement with Kim Jong Il's government in Pyongyang.

Many South Koreans still emphasize the importance of the U.S. alliance, forged in repelling the 1950 invasion from the North. Opponents of President Roh Moo Hyun view a warming to Pyongyang, and rising anti-Americanism here, as dangerous for the long-term security of South Korea.

South Koreans appeared in a state of shock over Kim's death. The news arrived at about 2 a.m., meaning the nation woke up to newspapers blaring headlines of false hope that his execution had been stayed. That hope was based on rumors circulating Tuesday that Kim's captors, a group said to be linked to al Qaeda, had delayed killing him.

As Roh stuck by his pledge to dispatch troops, lawmakers were demanding that the government clarify its handling of Kim's kidnapping. Statements by Kim's South Korean employers in Iraq -- which supplied food and clothing to the U.S. military -- indicated that U.S. authorities may have been aware of the kidnapping before South Korea's announcement last Friday that it would deploy its main contingent of troops in August.

The South Korean Foreign Ministry said on Wednesday that Kim apparently was kidnapped at the end of May, rather than on June 17, as initially reported. The North American bureau of the Foreign Ministry, according to the semi-official Yonhap News Agency, learned about the kidnapping from CNN. Al-Jazeera, the Arabic satellite television channel, first broadcast a tape of the hostage on Sunday. [On Thursday, Roh ordered a full investigation into the case in response to new disclosures, the Reuters news agency reported.]

A bipartisan group of 50 South Korean lawmakers signed a petition on Wednesday calling for the government to "halt and reconsider the additional dispatch" of troops. Experts said the measure was unlikely to muster immediate support in the National Assembly, but legislators are set to vote in September on extending the deployment beyond this year.

"If the U.S. kept information from us because they feared the information might have a negative effect on the dispatch, then that was cowardice," said Song Young Gil, a legislator from the Uri Party allied to Roh. "No matter what the reasons were, it is nonsense that they expect us to be the third largest allied country to send troops, when they cannot provide trust to an ally nation. The U.S. has totally lost its credibility by this behavior in the eyes of the Korean public."

Special correspondent Joohee Cho contributed to this report.

South Koreans mourn Kim Sun Il, shown in school portrait, who was beheaded by extremists in Iraq. Another woman at the rally in Seoul holds a poster tying President Bush to "murder."