SEOUL, South Korea (AP) -- South Korean lawmakers embarked on a diplomatic mission for the United States on Thursday to urge Washington to help negotiate the release of 21 hostages held by the Taliban.

The delegation from four major political parties, a nonpartisan showing of solidarity amid the crisis, is the latest South Korean attempt to persuade the United States to make an exception to its policy of refusing concessions to terrorist demands.

The Taliban kidnapped 23 South Koreans from a bus in southern Afghanistan on July 19 and has shot two of them to death. The group has threatened more killings unless the Afghan government releases insurgent prisoners.

Previous diplomatic efforts -- including sending a presidential envoy to Afghanistan and phone calls between President Roh Moo-hyun and Afghan President Hamid Karzai -- have failed to bend the Afghan government's refusal to respond to Taliban demands, concerned it could encourage more kidnappings.

The U.S. and other countries strongly condemned Afghanistan earlier this year when it released Taliban prisoners in exchange for a captive Italian journalist.

Seoul conceded Tuesday that it was limited in its ability to influence Kabul and turned to the United States for help, amid perceptions that it is ultimately Washington that can influence the Afghan government.

Relatives of the hostages took their pleas Wednesday to the U.S. Embassy, where officials promised to convey their message to Washington.

At a regional Asia security conference in the Philippines, South Korean Foreign Minister Song Min-soon and U.S. Deputy Secretary of State John Negroponte agreed to place top priority on safely freeing the hostages, ruling out a military option for ending the standoff.

"The United States is not preparing military operations," a South Korean Foreign Ministry official said after the meeting. He asked not to be named, citing the sensitivity of the issue.

The eight leading members of South Korea's parliament who departed Thursday for Washington hope to meet U.S. House Speaker Nancy Pelosi, Undersecretary of State Nicholas Burns and national security adviser Stephen Hadley.

In a joint statement, the lawmakers asked the U.S. government to take an "active and positive attitude to prevent the loss of human lives."

The delegation also plans to meet U.N. Secretary-General Ban Ki-moon, South Korea's former foreign minister.

Separately, 36 other lawmakers issued a joint statement urging Washington to make an exception to its policy on dealing with terrorists.

"It is a grim reality that the issue of releasing prisoners totally depends on the U.S. will," the statement said.

South Korea's presidential office has also called on the international community to exercise "flexibility" in handling the crisis.

Washington also faces a dilemma as its own as continued refusal to heed South Korean appeals could lead to a new wave of anti-U.S. sentiment in its key Asian ally, where some 29,000 American troops are based as a deterrent to North Korea.

In its first reaction to the hostage crisis, North Korea condemned the kidnappings and called for a peaceful end to the standoff.

"We hope that South Koreans kidnapped in Afghanistan could return home safely," Jong Song Il, deputy director general of North Korea's Foreign Ministry, told reporters late Wednesday in Manila, where he was accompanying North Korean Foreign Minister Pak Ui Chun to the security conference.

"It is the consistent stance that our republic is opposed to all kinds of terrorism," Jong said.

North Korea remains on a U.S. list of terrorism-sponsoring states following its alleged involvement in the 1987 bombing of a South Korean airliner, although it has since not been tied to any terrorist attack.