US Special Representative Sung Kim arrived in the South Korean capital on Monday for a five-day visit that has included talks with the outgoing president, Moon Jae-in, and members of the new administration preparing for office.

The visit comes after North Korea restarted tests of intercontinental ballistic missiles, breaking a self-imposed 2017 moratorium, and has shown signs that it may be preparing to resume nuclear testing.

Yoon will head a conservative administration and he has already signalled a tougher approach towards North Korea after efforts by the liberal Moon to improve ties failed to make headway.

Yoon and the US envoy met on Tuesday evening for dinner, their first encounter since Yoon won an election last month.

“It was a friendly get-together, not intended to discuss serious policy issues such as the North’s nuclear programme,” said the source in Yoon’s transition team who declined to be identified, citing diplomatic sensitivity.

Yoon’s nominee for foreign minister, Park Jin, met Kim on Wednesday.

Park said he hoped for an early summit between Yoon and President Joe Biden and vowed to expand cooperation over the North’s missile launches and possible nuclear tests, South Korea’s Yonhap news agency said.

Kim said on Monday that the allies would maintain the “strongest possible joint deterrent” and respond “responsibly and decisively” to North Korea’s “provocative behaviour”.

Kim has repeatedly offered to meet North Korean officials without preconditions but North Korea has brushed off the overtures, accusing the US of maintaining a hostile policy including sanctions and military exercises.

The US has some 28,000 troops in South Korea.

South Korean and US troops began annual joint military exercises this week. North Korea routinely denounces such drills as preparations for war on it.