In a press statement, received by Aljazeera.net, the DLP said there would be "outrage in the whole nation if they (the government) insists on the military deployment while seeing a citizen's life at stake".
The Foreign Ministry on Monday said it would go ahead with its plan to send more than 3000 troops to Iraq despite a televised threat from an Iraqi resistance group to kill a South Korean captive.
Thirty-three year old businessman, Kim Sun-il, has been shown repeatedly on South Korean television pleading for his life.
He was seized in Falluja on 17 June - the day before South Korea announced where its troops would be deployed after months of agonising because of security concerns and public opposition.
The DLP has urged the administration of President Roh Moo-hyun to "expeditiously exercise all available means and measures to open diplomatic channels and spare no sweat to have Kim Sun-il return alive."
The group holding Kim said South Korea had 24 hours from Sunday night to withdraw its decision or they would kill him, Aljazeera satellite channel reported.
The opposition party, which stressed it was against sending its troops to Iraq in the first place, urged the government to bear in mind that "if we keep insisting on any more military deployment, we will end up encountering even more troublesome disasters than we experience now."
Domination and oil
The Korean Network Against Dispatching Troops to Iraq, an umbrella organisation representing 365 Korean organisations, lent its weight to the calls.
In a statement, the network stated "the Korean people are well aware of the fact that the US invaded Iraq for domination and oil, and not for the freedom and peace of the Iraqi people."
Up to 3600 S Korean soldiers
will be sent to Iraq
"We also know that the US occupation of Iraq has denied the Iraqi people their sovereignty and that there have been widespread human rights abuses by US forces there, leading to Iraqi pain and loss of life."
"For this reason," the network added, "we have done all that is humanly possible to prevent the deployment of Korean troops, as they will in no way contribute to the peace and security of the Iraqi people."
The network added that it felt "the kidnapping and threatening a private citizen with death, however, will not contribute to Iraqi peace." The Iraqi people, the statement added, "are right to resist the US's unjust invasion, occupation and carnage".
Nevertheless, "kidnapping and threatening a private citizen with death cannot be justified," it added.
In the video footage aired on television, Kim is seen pleading for his life, saying "Korean soldiers, get out of here. I don't want to die. I don't want to die."
South Korea has said it will send 3600 troops to Iraq.