US State of Secretary John Kerry held a meeting with top South Korean officials on Monday following North Korea’s ballistic missile test and the execution of its defence chief.
Kerry met with President Park Geun-Hye in Seoul and touched on North Korean violations international law, such as undertaking provocative nuclear activities.
Kerry also spoke against North Korea’s cyberspace activities.
Kerry called the North's behaviour in the region “provocative”, “destabilising” and “unacceptable.”
Despite UN sanctions on North Korea banning it from using ballistic missile technology, North Korea announced last week that it successfully carried out a submarine-launched ballistic missile (SLBM) test.
The US has requested denuclearisation talks for three years but North Korea rejects all such invitations, labelling the whole effort as a provocation.
Kerry said "all they are doing now is isolating themselves further and creating greater risks to the region and to their own country."
He also added that the US still aims to sit down at the table with North Korea.
"We .... have some indication from the leader of North Korea that they are serious about engaging on the subject of their nuclear program."
Kerry also touched upon latest execution of North Korea's Defence Minister Hyon Yong-chol on 30 April by anti-aircraft fire in front of an audience.
Yong-chol was allegedly disloyal to the North Korean administration of Kim Jong Un.
Kerry described the killing as one among a series of "grotesque, grisly, horrendous, public displays of executions on a whim and fancy."
South Korean Foreign Minister Yun Byung-se said that it is inevitable to boost cooperation between South Korea and the US against recent threats and provocations by North Korea.
During his Beijing visit Kerry said that reaching a final nuclear deal with Iran may encourage North Korea to attend negotiations with six world powers regarding its nuclear programme.
The six world powers in question are North and South Korea, Japan, the United States, China and Russia, the group has not met for seven years.
The six countries have demanded North Korea give up its nuclear weapons in exchange for economic and diplomatic benefits, and security guarantees.
Kerry also to talked about cyber security issues late Monday after allegations that a series of cyber attacks were conducted by North Korean hackers against South Korean military institutions, banks, government agencies, TV broadcasters and media websites in recent years.
South Korea claims North Korea has an elite cyberwarfare unit comprising more than 6,000 personnel which creates a major security threat with its hacking capabilities.
Last year, the US accused North Korea of hacking Sony Pictures during the lead up to the release of the satirical film "The Interview," in which Kim Jong Un is killed by American journalists.
North Korea has denied responsibility for the cyber attacks against Sony Pictures but strongly condemned the movie due to its depiction of the assassination of Kim.