North Korea has conducted a record number of such tests this year, and also fired hundreds of artillery shells into the sea more recently as South Korea and the United States staged exercises, some of which involved Japan.
Cross-border rail operation between the two countries had been suspended since April 29, following a lockdown in Dandong attributable to the spread of Covid-19.
Talks with North Korea should not be for political show but contribute to establishing peace, South Korean President Yoon Suk-yeol said on Wednesday, just hours after the North test fired two cruise missiles into the sea.
On Saturday, Jo Yong Sam, director general at the North Korean Foreign Ministry's press and information affairs department, slammed Pelosi over her visit to the border and discussion of anti-North Korean deterrence.
Despite the Biden administration's vow to break a stalemate in denuclearisation talks with North Korea with practical approaches, no progress has been made since he came into office in early 2021.
The first public admission of COVID infections highlights the potential for a major crisis in a country that has refused international help with vaccinations and kept its borders shut.
Unlike outgoing President Moon Jae-in, who saw North Korea as a negotiating partner, incoming leader Yoon Suk-yeol sees the country as an adversary, said Cheong Seong-chang of the Center for North Korea Studies at the Sejong Institute.
The ongoing COVID wave, declared last week, has fuelled concerns over a lack of vaccines, inadequate medical infrastructure and a potential food crisis in the country of 25 million, which has refused outside help and kept its borders shut.
A senior Biden administration official told reporters on Saturday that the two leaders will discuss nuclear cooperation and that Washington remains ready for diplomacy with North Korea.
Neither president's approach has led to a major breakthrough, however, and North Korea has resumed testing its largest intercontinental ballistic missiles (ICBMs), while intelligence reports suggest it is preparing for a new nuclear test.