Thousands of South Koreans working for the US Forces Korea (USFK) were furloughed indefinitely starting Wednesday amid a deadlock in defense cost-sharing negotiations between the two countries, sparking concerns over the possible impact on Korea's readiness posture.

The furloughs have also drawn criticism that Washington is risking the livelihoods of South Koreans who have worked many years for the USFK for the sake of its own financial interests and to pressure its ally in the defense cost talks.

South Korea and the United States have failed to bridge differences over a new Special Measures Agreement (SMA) that stipulates how much Seoul would pay for the upkeep of the 28,500-strong USFK.

"Today, approximately half of the USFK Korean National employee workforce has been furloughed due to a lapse in the Special Measures Agreement," USFK Commander Gen. Robert Abrams said in a message to the furloughed employees.

Salaries of about 9,000 workers are covered by the agreement.

In a notice sent to the workers subject to the unpaid leave last week, the US Department of the Army said the furloughs would be in effect until further notice.

It is the first time that such a measure has been implemented since the establishment of the command.

Those who continue to work in areas of life, health, safety and other essential services will be paid by the US government, as the Pentagon earlier pledged.

Calling the situation "unfortunate," "unthinkable" and "heartbreaking," Abrams pledged to support the workers and to continue emphasizing to both the US and South Korean governments the need for a deal to end the furloughs.

"While this is an unfortunate situation and we will miss them dearly, we will work to minimize the impact on our 'fight tonight' posture despite the strenuous circumstances," Abrams said, calling the workers "vital to our mission and the Korea-US alliance.

The impact may be worse as installation services have already been partially halted and soldiers' off-installation travel has been restricted due to the COVID-19 virus.

During the latest and seventh round of talks last month, South Korea proposed concluding a separate agreement to first address the wage issue, but the US rejected the idea over concerns that such a move could further delay a comprehensive deal, Seoul's top negotiator Jeong Eun-bo has said.

Critics said the US has been using the issue as leverage in the negotiations.

On Tuesday, Jeong expressed regret over the furloughs and called on Washington to strive for the employees' swift return to work.

But Jeong also said that the two countries "have considerably narrowed differences, we expect the final conclusion of the negotiations in the near future."

On Wednesday, a diplomatic source also said that Seoul and Washington could announce a deal as early as later in the day, as they have reached "the stage of putting the finishing touches on the negotiations."

The US has reportedly demanded a hefty increase in Seoul's financial contribution, while Seoul appears to have expressed its willingness to pay more than its earlier proposal of an approximate 10 percent increase.

The previous one-year SMA expired at the end of 2019. Under the deal, South Korea agreed on an 8.2 percent increase.

Meanwhile, the USFK Korean Employees Union representing about 8,600 local workers of the USFK called for rapid normalization of the situation in a news conference on Wednesday, estimating about 4,000 of its members have gone on unpaid leave.

"The livelihoods of (Korean) workers have been hit hard by the collapse of the talks with the US, particularly at a time when it is difficult to find day labor or part-time jobs due to the new coronavirus outbreak. This will also have a clear impact on the local economy around US bases," the union said at the conference held in front of the US Army Garrison Humphreys in Pyeongtaek, 70 kilometers south of Seoul.

"The US's unreasonable demand for Korea's increased share of the defense costs is to abandon the bilateral alliance and will trample the noble spirit of the USFK and its workers practicing a pure Korean-US alliance," the union said, urging the Seoul government to request a thorough system reform in negotiations to prevent recurrence of a similar situation.

The union then raised expectations that the Korean government will soon announce support measures for its workers put on unpaid leave. (Yonhap)