North Korea has called US House Speaker Nancy Pelosi "the worst destroyer of international peace and stability," accusing her of inciting anti-North Korea sentiment and enraging China during her Asian tour.
Ms Pelosi travelled to South Korea after visiting Taiwan, which had prompted China to launch military exercises including missile strike training in waters near the self-governed island.
China views Taiwan as part of its own territory, to be annexed by force if necessary.
While in South Korea, Ms Pelosi visited a border area with North Korea and discussed the North's nuclear program with South Korean National Assembly Speaker Kim Jin-Pyo.
According to Mr Kim, the two agreed to support their respective governments' push for denuclearisation and peace on the Korean Peninsula based on diplomacy and strong, extended deterrence against North Korea.
The director-general at the North Korean Foreign Ministry's press and information affairs department slammed Ms Pelosi over her visit to the border and her discussion of anti-North Korean deterrence.
"Pelosi, who had come under a volley of due criticism from China for destroying regional peace and stability by visiting Taiwan, stirred up the atmosphere of confrontation with North Korea during her stay in South Korea," the director-general said in a statement carried by state media.
Calling her "the worst destroyer of international peace and stability", North Korea said Ms Pelosi's behaviour in South Korea had clearly shown hostility towards the North by the administration of US President Joe Biden.
"It would be a fatal mistake for her to think that she can go scot-free in the Korean Peninsula," the foreign ministry said.
"The US will have to pay dearly for all the sources of trouble spawned by her wherever she went."
Tensions remain high on Korean Peninsula
Nancy Pelosi's visit to the Joint Security Area at the Korean border made her the highest-profile American to go there since then-president Donald Trump visited in 2019 for a meeting with North Korean leader Kim Jong Un.
Located inside the world's most heavily fortified border, the area is jointly controlled by the American-led United Nations Command and North Korea.
US presidents and other top officials have previously travelled to the area to reaffirm their security commitment to South Korea in times of tension with North Korea.
During her visit, Ms Pelosi did not make any strong public statements against North Korea.
She uploaded several photos from the JSA on Twitter and wrote: "We conveyed the gratitude of the Congress and the country for the patriotic service of our service members, who stand as sentinels of democracy on the Korean Peninsula."
Tensions on the Korean Peninsula remain high after North Korea's run of missile tests earlier this year. US and South Korean officials said North Korea was ready to carry out its first nuclear weapons test in five years.
North Korea has said it would not return to denuclearisation talks and will instead focus on expanding its nuclear program unless the United States drops its hostile policies, in an apparent reference to US-led international sanctions on the North and its regular military drills with South Korea.
After Ms Pelosi visited Taiwan and reaffirmed Washington's commitment to defending democracy on the self-governing island, North Korea on Wednesday issued a statement berating the US and supporting China, its main ally and biggest aid benefactor.