Donald Trump has ordered the Pentagon to prepare options for drawing down US troops in South Korea, just weeks before he holds a landmark meeting with North Korea’s leader, Kim Jong-un, according to several people briefed on the deliberations.

Reduced troop levels are not intended to be a bargaining chip in Mr Trump’s talks with Mr Kim about his weapons programme, these officials said. But they acknowledged that a peace treaty between the two Koreas could diminish the need for the 23,500 soldiers stationed on the peninsula.

Mr Trump has been determined to withdraw troops from the region, arguing that the United States is not adequately compensated for the cost of maintaining them, that the troops are mainly protecting Japan and that decades of US military presence had not prevented North Korea from becoming a nuclear threat.

His latest push coincides with tense negotiations with South Korea over how to share the cost of the military force. Under an agreement that expires at the end of 2018, South Korea pays about half the cost of the upkeep of the soldiers – more than $800m (£600m) a year. The Trump administration is demanding that it pay for virtually the entire cost of the military presence.

The directive has rattled officials at the Pentagon and other agencies, who worry that any reduction could weaken the US alliance with South Korea and raise fears in neighbouring Japan at the very moment that the United States is embarking on a risky nuclear negotiation with North Korea.

Officials declined to say whether Mr Trump was seeking options for a full or partial reduction of troops, although a full withdrawal was unlikely. They emphasised that rethinking the size and configuration of the US force was overdue, regardless of the sudden flowering of diplomacy with North Korea.

But Mr Trump’s meeting with Mr Kim injects an unpredictable new element. His enthusiasm for the encounter – and the prospect of ending a nearly 70-year-old military conflict between the two Koreas – has raised concerns that he may offer troop cuts in return for concessions by Mr Kim.

Defence secretary James Mattis added to those concerns last Friday when he suggested that the future of the US military presence might be on the table.

For Mr Trump, withdrawing troops would have multiple benefits, said Victor Cha, a Korea scholar at Georgetown University who was for a time under consideration to be ambassador to Seoul. It would appeal to his political base, save the United States money and give him a valuable chit in his negotiation with Mr Kim.

“But from the perspective of the US-South Korea alliance,” Mr Cha said, “it would represent a major retrenchment”.

Kelly E Magsamen, a top Asia policy official at the Pentagon during the Obama administration, said, “US presence in South Korea is a sacrosanct part of our alliance”.

The South Korean government reiterated this week that the troops were still needed and would not be pulled out as a result of a peace treaty with North Korea. But even close allies of president Moon Jae-in have raised doubts about the rationale for a long-term US presence.

“What will happen to US forces in South Korea if a peace treaty is signed?” Moon Chung-in, an adviser to the president, said in a widely read article published this week. “It will be difficult to justify their continuing presence.”

North Korea Military Parade Show all 6 1 /6 North Korea Military Parade North Korea Military Parade In this image made from video released by KRT on Feb. 8, 2018, a military parade is held at Kim Il Sung Square in Pyongyang, Thursday, Feb. 8 2018, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade This screen grab taken from North Korea's KCTV on February 8, 2018 shows members of North Korea's military taking part in a parade, with missiles being displayed, in Kim Il Sung Square in Pyongyang. North Korea staged a military parade in Pyongyang on February 8 to mark the 70th anniversary of its armed forces, in a show of strength just a day before the Pyeongchang 2018 Winter Olympic Games open in the South. / AFP PHOTO / KCTV / KCTV / -----EDITORS NOTE --- RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / KCTV" - NO MARKETING - NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS - NO ARCHIVESKCTV/AFP/Getty Images AFP/Getty Images North Korea Military Parade In this image made from video released by KRT, North Korean soldiers march during a military parade in Pyongyang, Thursday, Feb. 8 2018. North Korea held a military parade and rally on Kim Il Sung Square on Thursday, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade In this image made from video released by KRT on Feb. 8, 2018, North Korean leader Kim Jong Un, right, inspects honor guards, along with his wife Ri Sol Ju, center, during a military parade in Pyongyang, Thursday, Feb. 8 2018. North Korea held a military parade and rally on Kim Il Sung Square on Thursday, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade In this image made from video released by KRT on Feb. 8, 2018, North Korean leader Kim Jong Un, center, watches the military parade in Pyongyang, Thursday, Feb. 8 2018. North Korea held a military parade and rally on Kim Il Sung Square on Thursday, just one day before South Korea holds the opening ceremony for the Pyeongchang Winter Olympics. (KRT via AP Photo) AP North Korea Military Parade This screen grab taken from North Korea's KCTV on February 8, 2018 shows North Korean leader Kim Jong Un speaking during a military parade in Kim Il Sung Square in Pyongyang. North Korea staged a military parade in Pyongyang on February 8 to mark the 70th anniversary of its armed forces, in a show of strength just a day before the Pyeongchang 2018 Winter Olympic Games open in the South. / AFP PHOTO / KCTV / KCTV / -----EDITORS NOTE --- RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / KCTV" - NO MARKETING - NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS - NO ARCHIVESKCTV/AFP/Getty Images AFP/Getty Images

Mr Kim recently declared, through South Korean officials, that he would drop North Korea’s long-standing insistence that US troops leave the peninsula. Some experts argue that watching US soldiers depart is far less important to him than winning relief from economic sanctions.

For years, the US presence has been more important as a symbol of deterrence than as a fighting force. At their current levels, the troop numbers are down by about a third from the level in the 1990s.

As the South Koreans have become a premier fighting force – with their own special operations forces, the ability to oppose North Korea’s artillery along the Demilitarized Zone and now their own cyber forces – they have become less dependent on the United States. Most US troops have pulled back to well south of Seoul.