The US military flew two strategic bombers over the Korean peninsula in a show of force late on Tuesday, as President Donald Trump met top defence officials to discuss how to respond to any threat from North Korea.
The two B-1B bombers were accompanied by two F-15K fighters from the South Korean military after leaving their base in Guam, the South's Joint Chiefs of Staff said in a news release on Wednesday.
Officials feared the rogue nation would test another missile or nuclear bomb on Monday or Tuesday as North Korean citizens celebrated the 11th anniversary of the country's first nuclear test and the foundation of the ruling Worker's Party of Korea.
North Korea has launched two missiles over Japan and conducted its sixth and biggest nuclear test in recent weeks in defiance of U.N. sanctions as it races towards its goal of developing a nuclear-tipped missile capable of hitting the United States.
Visits by US warships and bombers along with regular joint exercises with the South infuriate North Korea, which considers them a sign of aggression and a rehearsal for an invasion.
The US bombers had taken off from the Andersen Air Force Base in Guam.
Russian state news agency Tass says North Korea's foreign minister has described his nation's nuclear weapons as a "sword of justice".
But the contingency plan for the South's special forces was stolen, he said, as well as details about annual joint military drills with the USA and information on key military facilities and power plants.
US and South Korean wartime operational plans, including a plan to wipe out the North Korean leadership, were stolen by North Korean hackers past year, a South Korean ruling party lawmaker said on Wednesday. The US has repeatedly ruled out negotiations with North Korea.
Some 235 gigabytes of military documents were taken from South Korea's Defence Integrated Data Centre in September past year, Democratic Party representative Rhee Cheol-hee said in radio appearances on Wednesday, citing information from unidentified South Korean defence officials.
A spokesman from South Korea's Defense Ministry declined to comment, saying the information is classified.
Tensions between the U.S. and North Korea have intensified in recent months as the Trump administration has struggled to rein in Kim Jong-un's expanding nuclear and ballistic weapons programme.
The secretive state has been suspected of carrying out cyber attacks on South Korean electric utilities as well as on other government and financial institutions.
Fears the crisis could spiral into open conflict have risen as the communist state demonstrated rapid progress in its efforts to develop a nuclear-tipped missile that could target the US mainland despite several rounds of punishing United Nations and other global sanctions against it.
And while there are many in Washington who are willing to explore the possibility of talks, it is less clear whether President Donald Trump will personally be in favor of a former United States leader taking the spotlight.