SEOUL, Jan 6 (Reuters) - South Korea's government said

on Monday it will extend the shutdown of Muan International

Airport by a week to Jan. 14, citing the ongoing investigation

into the crash of a Jeju Air jet that killed 179

passengers on board.

The airport had been due to reopen on Tuesday following

the Dec. 29 crash.

A joint investigation team is stepping up the probe into

South Korea's deadliest air accident. Two of the Korean

investigators on Monday are set to leave for the United States

with flight data recorders for analysis with the U.S. National

Transportation Safety Board.

The flight data recorders, along with cockpit voice

recorders, are the two black boxes that contain key information

about the crash.

Investigators on Saturday compiled the complete

transcript from the cockpit voice recorder recovered from the

wreckage of the Jeju Air Boeing 737-800. It is not

clear whether they will disclose the transcript.

Investigators retrieved two of the plane's engines over

the weekend, as a representative from engine maker GE

joined

the probe. The transport ministry

extended

to Jan. 10 its inspections of all the Boeing 737-800 planes

operated by Jeju Air and five other airlines in the country,

including their maintenance records.