The United States has not ruled out using military force to free 21 South Korean captives held by the Taliban in Afghanistan, a senior State Department official said Thursday.

But the remarks by Richard Boucher, assistant secretary of state for South and Central Asia, seemed to conflict with a South Korean official who said that both countries had ruled out military intervention.

Meantime, an Afghan mediator said South Korean and Afghan officials have agreed to meet face-to-face with the Taliban to discuss the release of the captives but are still negotiating a suitable location.

"All pressures need to be applied to the Taliban to get them to release these hostages," said Boucher. "We hope that pressure can be effective in a variety of ways, the goal is to get these people released unharmed, to get them released peacefully and safely.

"We will all make efforts together to try to encourage that," he told reporters at the State Department.

He did not elaborate on what pressure was being used but said it included the option of military force.

"There are things that we say, things that others say, things that are done and said within Afghan society as well as potential military pressures," Boucher said

However one South Korean official said that Seoul's foreign minister, Song Min-Soon, and Deputy Secretary of State John Negroponte had agreed during a meeting earlier Thursday in the Philippines to rule out a military attempt to end the standoff.

On the 15th day of the hostage crisis Thursday, an eight-person delegation of South Korean legislators travelled to the U.S. to implore Washington to step in and help in diplomatic efforts to free the hostages.

South Koreans rally outside the U.S. embassy in Seoul on Thursday in support of 21 remaining hostages taken captive in Afghanistan.
(Anthony Germain/CBC)

The lawmakers are expected to meet with House Speaker Nancy Pelosi, Undersecretary of State Nicholas Burns and national security adviser Stephen Hadley. They also planned to meet UN Secretary-General Ban Ki-moon, South Korea's former foreign minister.

"We will sincerely plead with the United States to take more substantial and meaningful measures to resolve this crisis," Rep. Cheon Young-se of the Liberal Democratic Labour Party said before the delegation set off.

In Seoul, parents of the remaining 21 Christian aid volunteers grieved over the death of Shim Sun-min, the 29-year-old executed on Monday. His bullet-ridden corpse was found by the side of a road, making Shim the second hostage to have been killed so far since gunmen seized the group July 19. The Taliban have vowed to kill more.

"Please, please help us," Kim Taek-Kyung, the mother of one of the hostages, Han Ji Young, pleaded from the South Korean capital. "I want to go to Afghanistan and on my knees ask the Taliban to exchange for my daughter. She is young; I am old. I want her to live," she said.

Waheedullah Mujadidi, the chief negotiator in dealing with the Taliban, told the Associated Press the captors had agreed to meet with South Korea's ambassador but have yet to decide where the meeting should take place.

A purported Taliban spokesman has said the Taliban's key demand is the release of militant prisoners in exchange for the lives of the South Koreans. He also claimed that two of the female hostages were ill and may be close to death.

South Korean President Roh Moo-hyun has spoken by phone with Afghan President Hamid Karzai, but the Afghan government has steadfastly refused to free any jailed insurgents, fearing it could encourage more kidnappings.

On Wednesday, Afghan army helicopters dropped leaflets warning of impending military action on Ghazni province, where it is thought the hostages are being held. But a Defence Ministry spokesman later said the operation had no connection with the hostage crisis.

With files from the Associated Press