Trump has vowed to "properly deal" with Pyongyang, and the US House of Representatives has overwhelmingly approved legislation tighten sanctions on North Korea by targeting its shipping industry and companies that do business with the reclusive state.
The date of the alleged assassination attempt is unclear; however, Kim Jong Un presided over a military parade on April 15.
China's envoy to the United States, Cui Tiankai, conveyed the request to the USA side, to coincide with the first face-to-face, two-day meeting between President Donald Trump and Xi in Florida from April 6, but the Trump administration likely rejected it, the source said.
Pyongyang criticized South Korea in 2012, alleging that Seoul had sent a North Korean defector back to blow up statues of North Korean founder Kim Il Sung with remote-controlled explosives.
South Korea's defence ministry said it did not have an immediate comment on the report. Goods produced by North Korea's forced labor would be prohibited from entering the United States, according to the legislation.
The North's Ministry of State Security said terrorism is a common enemy to humankind, but the communist country is blamed for a terrorist attack that killed the estranged half brother of North Korean leader Kim Jong-un. The tensions mainly stem from North Korea's pursuit of nuclear and missile development programmes in defiance of global warnings.
Le Pen tells AP she 'changed everything'
And critics decried the bitter tone of Wednesday night's presidential debate . "I'm not going to lament our democracy", he said. Le Pen's father has minimized the Holocaust and her National Front party has been stained by anti-Semitism in the past.
The plot included the use of "biochemical substances including radioactive substance and nano poisonous substance" whose results would "appear after six or twelve months", the statement said. It is also holding at least three Americans on charges of "hostile acts", including a Korean-American named Kim Dong-chul, whom it accused of spying for the South.
Analysts said the accusations could be a pre-emptive attempt to try to dissuade Washington from any attempt at a surgical strike on its leadership, as suggested by some commentators. North Korea denied involvement.
That was the latest salvo in the Trump administration's push to get the global community to intensify diplomatic and economic pressure on North Korea to dismantle its nuclear weapons program before it can pose a direct threat to the American mainland.
On Friday, a spokesman for North Korea's Foreign Ministry called Gardner's remarks a "provocation that can not be overlooked" and an affront to the dignity of the country's supreme leadership, from a man who was "tantamount to mentally deranged".
The visit was highly symbolic since the islets are near Yeonpyeong Island, which was the site of a deadly North Korean artillery attack in 2010 - one of the most serious incidents between the two countries since the Korean War ended in 1953.