Jeong Eun-bo, Seoul's chief negotiator, arrived in Washington on Monday for talks with his American counterpart, James DeHart.
The negotiations are slated to run for two days through Wednesday.
The US has reportedly demanded that South Korea increase its contribution fivefold to nearly $5 billion next year. Under this year's deal, called the Special Measures Agreement, Seoul agreed to pay $870 million, an increase of 8.2 percent from last year.
In London, US President Donald Trump made his position clear that South Korea "should burden-share more fairly," saying it is up for debate whether keeping 28,500 American troops in that country is in the US national security interest.
Trump is in the British capital to attend a meeting of North Atlantic Treaty Organization leaders.
"(Trump) has always said that (South Korea) should pay more, so I don't think there has been a big change in terms of the situation," Jeong told reporters upon arriving at the State Department to meet with the US team.
He refused to answer when asked what alternatives the South Korean side came prepared with.
The previous round of negotiations in Seoul last month was cut short after the US side walked out, citing South Korean proposals that "were not responsive to our request for fair and equitable burden sharing."
Later in the day, Jeong was asked by reporters whether the possibility of a troops reduction was discussed during the morning session.
"Not at all," he answered. "It's going well."
Last month, the South Korean daily, Chosun Ilbo, reported that the US is considering withdrawing a brigade from South Korea in the event that Seoul refuses to accept Washington's demand in the cost-sharing negotiations.
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)