WASHINGTON -- A US Joint Chiefs of Staff official said Wednesday that he is not aware of any discussion inside the Pentagon of a possible drawdown of American troops in South Korea.

Speculation of a possible reduction of the 28,500-strong US Forces Korea has grown in recent weeks amid tough negotiations on how the allies will share the costs for the troops' upkeep.

US President Donald Trump added to the uncertainty on Tuesday when he told reporters in London that the benefit of continuing the US military presence in its current state is up for debate.

"I know of no discussions within the Pentagon that talks about any type of drawdown in, reduction of forces or anything like that," Rear Adm. Jeffrey Anderson, deputy director for political-military affairs for Asia on the Joint Staff, said at a conference discussing the South Korea-US alliance.

"That said, we're always assessing the effectiveness of our organizational structure," he added. "That's a continuous thing that militaries throughout the world do. But there's certainly no discussions that I know of regarding a reduction."

Trump's comment on Tuesday came as Seoul and Washington have been negotiating a new cost-sharing deal for next year. The US has reportedly demanded a fivefold increase in South Korea's contribution to nearly $5 billion.

Trump said on the continued US troop presence that he thinks "if we're going to do it, I think it's -- you know, they should burden share more fairly."

The comments suggested the US president was using the threat of a troops reduction to clinch a favorable deal in the cost-sharing negotiations that have been under way in Washington Tuesday and Wednesday.

Last month, a South Korean newspaper reported that the US is considering withdrawing a brigade from South Korea in the event that Seoul refuses to accept Washington's demands for burden-sharing.

The Pentagon dismissed the report as having "absolutely no truth."

US Defense Secretary Mark Esper also said he had not heard of such plans, adding, "We're not threatening allies over this. This is a negotiation." (Yonhap)