A free trade panel of South Korean lawmakers visited an inter-Korean joint industrial complex in the North Wednesday to promote the inclusion of the inter-Korean made products manufactured in North Korea into the free trade deal between Seoul and Washington, National Assembly officials said.

Eleven ruling and opposition party lawmakers, accompanied by about 170 aides and National Assembly officials, travelled to North Korea's border city of Kaesong to make a first-hand assessment of the first inter-Korean industrial complex, the officials said.

They crossed the border, using the overland route that cuts through the Demilitarized Zone separating the two Koreas.

The visit was made amid a sixth round of the free trade talks between South Korea and the United States, which opened in Seoul on Monday for a five-day run.

The Kaesong industrial complex is a pilot inter-Korean economic venture, in which South Korean businesses take advantage of inexpensive North Korean labor to produce goods. Some 20 South Korean factories employ about 11,000 North Korean workers in Kaesong.

Seoul wants to include for free trade agreeement (FTA)-covered products, while Washington balks at the idea of accepting products made in North Korean territory.

Panel members of the main opposition Grand National Party decided not travel together to the Kaesong industrial complex, saying "Including the Kaesong made products is not a decisive matter regarding the FTA."

During the one-day trip, they were briefed by industrial zone management and tour facilities of a few South Korean companies operating there and the construction site under development, the officials said.

"The Kaesong industrial complex is not simply an economic venture, but an important initiative for peace in the Korean peninsula," said the lawmakers in the statement, asking the negotiators from the U.S. and South Korea to include the Kaesong made products in the FTA.