North Korea has accused the United States of trying to undermine an improvement in inter-Korean relations.
"The two Koreas have co-operated together and the Olympics was held successfully," the North's KCNA news agency said, citing North Korea's foreign ministry.
"But the US brought the threat of war to the Korean peninsula with large-scale new sanctions on the DPRK ahead of the Olympics closing ceremony," the state news agency said, using the initials of the North's official name, the Democratic People's Republic of Korea.
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The Winter Olympics in South Korea have given a boost to engagement between the two Koreas after more than a year of sharply rising tension over the North's missile tests and its sixth and largest nuclear test in defiance of UN sanctions.
Kim Yo-jong, the younger sister of North Korean leader Kim Jong-un, led a delegation that made a three-day visit to the opening of the Olympics and the North Korean leader later said he wanted to boost a "warm climate of reconciliation and dialogue".
But the North's decision to send former military intelligence chief Kim Yong-chol as delegation leader to the closing ceremony has enraged families of 46 sailors killed in the torpedo attack on their ship.
The closing days of the Olympics were also overshadowed by a US announcement on Friday that it was imposing its largest package of sanctions aimed at getting North Korea to give up its nuclear and missile programs.
In announcing the sanctions, US President Donald Trump warned of a "phase two" that could be "very, very unfortunate for the world" if the sanctions did not work.
North Korea criticised the new sanctions in a statement carried on its state media and said a blockade by the United States would be considered an act of war.
China also reacted angrily to the new US measures, saying the unilateral targeting of Chinese firms and people risked harming co-operation on North Korea.