SEOUL - South Korea said Sunday it had agreed to pay about $866.6 million this year to keep on its soil US troops who help guard against threats from North Korea. Seoul’s foreign ministry, after months of negotiation with Washington, confirmed this year’s contribution of 920 billion won ($866.6 million), up 5.8 percent from last year. The two allies also agreed on a maximum 4 percent annual increase in the amount until 2018, the ministry spokesman Cho Tai-Young told reporters.The South and the US have since 1991 shared the cost of hosting American soldiers, currently numbered at around 28,000 - the legacy of 1950-53 Korean War. The latest agreement - the ninth since 1991 - is subject to a parliamentary approval in Seoul. “We tried to produce a reasonable result to persuade South Koreans and our lawmakers while taking into account our financial burdens as well as the conditions for stably hosting the US troops,” Cho said. The agreement came as the South girds for potential military provocations by the communist North after the shock execution of the leader Kim Jong-Un’s uncle.Kim last month purged the once-powerful Jang Song-Thaek for charges including corruption and treason in the biggest political upheaval since he took power two years ago. Seoul’s defence chief Kim Kwan-Jin as well as analysts have warned that the impoverished but nuclear-armed North may stage armed provocations early this year to cement domestic unity and rally support for Kim. The North has for decades criticised the presence of US troops stationed across the South, calling them a major hurdle for peace-building with Seoul. Pyongyang has consistently responded with anger to South Korea-US joint military exercises staged regularly below the border. In November 2010, in the most high-profile case, the North shelled a border island, killing four South Koreans in what it called a protest against the South-US military drills staged nearby.