South Korea could delay awarding an eight trillion won ($6.9 billion) contract for 60 advanced fighter planes, the arms procurement agency said Wednesday after setting a new deadline for bids.
The makers of Boeing's F-15 Silent Eagle, Lockheed Martin's F-35 Lightning II and the Eurofighter Typhoon had submitted bids when the original deadline expired Monday.
But the Defense Acquisition Program Administration (DAPA) reopened bidding Tuesday, citing what it called errors in the relevant documents, and set a new date of July 5 for submissions.
"Our plan to make a decision by the end of October is not a deadline, but a target," DAPA commissioner Noh Dae-Rae told Yonhap news agency in comments confirmed by a spokesman for the agency.
"We could delay the timing of selecting a supplier at any time if it is necessary for the national interest."
Controversy has erupted over plans to assess the performance of Lockheed's F-35 using simulators rather than actual test flights with the South's pilots.
Boeing and EADS, maker of the Eurofighter, agreed on real flights, but Lockheed refused to do so, saying its aircraft is still being developed, Yonhap quoted DAPA officials as saying.
They said DAPA had asked Lockheed for more Korean involvement in tests on the F-35.
Noh said the two sides have been discussing the proposal and the US firm would give its answer Friday.
"If the US side rejects our request, we will have no choice but to give a zero point in the criteria of flight-testing (of the F-35)," he said.
South Korea has bought 60 of Boeing's earlier-version F-15s since 2002 under the first two stages of its fighter modernisation programme.
Tensions with North Korea have been high in recent years. The North and South remain technically at war because a peace treaty was never signed formally to end their 1950-53 conflict.