US Defense Secretary Mark Esper said Monday he called South Korean Defense Minister Jeong Kyeong-doo to discuss the importance of an "equitable" defense cost-sharing agreement between the allies.

The phone call took place days after US Forces Korea placed thousands of Korean workers at US military bases on unpaid leave, citing the absence of an agreement to cover their salaries.

"I appreciate Korean Defense Minister Jeong taking my phone call today to discuss the importance of equitable burden sharing across the alliance," Esper tweeted.

"It is critical that we get a fair, balanced, and comprehensive agreement signed quickly," he said, adding the alliance's motto, "#KatchiKapshida," which in Korean means "Let's go together."

Seoul and Washington have held seven rounds of negotiations since September to try to renew the Special Measures Agreement, which stipulates South Korea's contribution to the cost of keeping 28,500 American troops stationed on the peninsula.

Under the previous SMA that expired at the end of December, Seoul was required to pay $870 million. This year, Washington has demanded a significant increase in Seoul's contribution, though it has reportedly backed down from its initial demand of $5 billion.

During the phone call, Jeong once again proposed settling the wage issue first, a South Korean defense ministry official said, referring to Seoul's proposal to first conclude a separate agreement dealing with the wage issue.

South Korea made the proposal during the latest round of talks last month, but the United States rejected the idea over concerns that it could further delay a new cost-sharing deal. Esper's reference to a "comprehensive" agreement appears to reflect Washington's opposition to a separate wage deal.

"Both sides shared the notion that they should reach a fair and mutually agreeable level, and consultations for the goal should continue," the defense ministry official said.

Last week, South Korean media reported that the two sides had reached a tentative agreement that could be announced as soon as last Wednesday.

No deal has been announced, with US officials insisting that negotiations are under way to ensure an equitable and mutually beneficial deal for both sides.

"(US President Donald Trump) has been clear in the expectation that our allies around the world, including South Korea, can and should contribute more," a State Department official said last week on condition of anonymity. (Yonhap)