South Korea and the United States struck a new deal on Sunday on how much Seoul should pay for the US military presence on its soil, officials said, after previous rounds of failed negotiations caused worries about their decades-long alliance.

Last year, South Korea provided about $830 million, roughly 40 per cent of the cost of the deployment of 28,500 US soldiers whose presence is meant to deter aggression from North Korea. President Donald Trump has said South Korea should pay more.

Read more:US, S. Korean diplomats meet in run-up to Trump-Kim summit

The allies had failed to reach a new cost-sharing plan during some 10 rounds of talks. On Sunday, Seoul's Foreign Ministry said the countries signed a new deal. A five-year 2014 deal that covered South Korea's payment last year had expired at the end of 2018.

Some conservatives in South Korea voiced concerns over a weakening alliance with the United States amid a stalemate in negotiations with North Korea to deprive it of its nuclear weapons.

They said Trump might use the failed military cost-sharing negotiations as an excuse to pull back some of US troops in South Korea, as a bargaining chip in talks with North Korean leader Kim Jong Un.

Trump told CBS' “Face the Nation” last Sunday that he has no plans to withdraw troops from South Korea.

Trump announced last week that he will sit down with Kim for a second summit in Hanoi, Vietnam in late February.

Their first summit in Singapore last June resulted in Kim's vague commitment to "complete denuclearisation of the Korean Peninsula," a term that his propaganda machine previously used when it argued it would only denuclearise after the US withdraws its troops from South Korea.

The South Korean ministry hasn't immediately revealed the exact amount of money Seoul would pay this year under the new deal.

Yonhap news agency reported that South Korea will provide about 1.04 trillion won ($924 million) in 2019. Yonhap said the US had previously demanded 1.13 trillion won ($1 billion) from South Korea.

The US military arrived in South Korea to disarm Japan, which colonised the Korean Peninsula from 1910-45, following its World War II defeat. Most US troops were withdrawn in 1949 but they returned the next year to fight alongside South Korea in the 1950-53 Korean War.

South Korea began paying for the US military deployment in the early 1990s, after rebuilding its war-devastated economy.

The big US military presence in South Korea is a symbol of the countries' alliance, forged in blood during the war, but also a source of long-running anti-American sentiments.