The US, Japan and South Korea have not killed North Koreans in the 21st century. Israel has killed about 170 North Koreans and injured 2000 in relations to nuclear weapons from an incident in 2004 and another in 2007. Note both actions occurred while George W Bush was president of the USA.
Israel is 8000 kilometers or 5000 miles from North Korea.
Israel would need to work with South Korea in order to have successful operations against North Korea.
Syrian reactor 2007
On September 6, 2007, Operation Orchard was an Israeli airstrike on a suspected nuclear reactor in the Deir ez-Zor region of Syria, which occurred just after midnight (local time) on September 6, 2007. 10 North Korean workers allegedly killed in the attack.
On March 19, 2009, Hans Rühle, former chief of the planning staff of the German Defense Ministry, wrote in the Swiss daily Neue Zürcher Zeitung that Iran was financing a Syrian nuclear reactor. Rühle did not identify the sources of his information. He wrote that U.S. intelligence had detected North Korean ship deliveries of construction supplies to Syria that started in 2002, and that the construction was spotted by American satellites in 2003, who detected nothing unusual, partly because the Syrians had banned radio and telephones from the site and handled communications solely by messengers. He said that “The analysis was conclusive that it was a North Korean-type reactor, a gas graphite model” and that “Israel estimates that Iran had paid North Korea between $1 billion and $2 billion for the project”. He also wrote that just before the Israeli operation, a North Korean ship was intercepted en route to Syria with nuclear fuel rods.
On November 19, 2008, IAEA released a report which said the Syrian complex bore features resembling those of an undeclared nuclear reactor and UN inspectors found “significant” traces of uranium at the site.
North Korean Train carrying nuclear materials in 2004
The Ryongchŏn disaster was a train disaster that occurred on April 22, 2004, in the town of Ryongchŏn, North Korea, near the border with the People’s Republic of China. Shortly after the incident, a Syrian airliner landed in North Korea, purportedly to deliver aid. However, they retrieved the bodies of Syrian citizens that had been in the explosion. The Red Cross was allowed into the area, in an unusual concession from the North Korean authorities, becoming the only outside agency to see the disaster area. According to the initial agency report, 160 people were killed and 1,300 were injured in the disaster.
A Mossad agent surreptitiously entered North Korea using a stolen Canadian passport, a massive explosion in a North Korean freight train carrying nuclear material killed at least a dozen Syrian nuclear scientists, and many more North Koreans. Israeli intelligence, which is thought to have played a role in the attack, reported that there was so much radioactive material onboard that the scientists were flown back to Syria in lead caskets.
The explosion destroyed 40 percent of the town and had the fingerprints of an Israeli intelligence operation. It was later discovered that a rigged cell phone triggered the blast, which also killed a dozen Syrian missile technicians working for the Syrian Center for Scientific Research.
During the 1973 Yom Kippur War, the Israeli air force’s first and last dogfights in the skies over Egypt involved North Korean pilots flying Soviet MIG fighters. North Korea sent 20 pilots and 19 non-combat personnel to Egypt during Yom Kippur War. The unit had four to six encounters with the Israelis from August through the end of the war.
Iranian scientists have been special guests at North Korean nuclear bomb tests. A delegation of Iranian scientists during North Korea’s 2013 nuclear tests heightened Israel’s security concerns, and further entrenched Israel’s opposition to North Korea’s nuclear buildup.
North Korea has trained and armed the Palestine Liberation Organization, Hamas and Hezbollah. One North Korean specialty—tunnel technology—is valued by Iran, which needs to protect its nuclear facilities against attack, and by Hamas and Hezbollah, who use it to infiltrate Israel.
A 2010 Congressional Research Service report revealed that North Koreans have helped Hezbollah build underground tunnels in Lebanon. These tunnels could act as strategically important weapons caches during a war with Israel.
The scale of ground-level cooperation between North Korea and Hezbollah has caused Israel to staunchly oppose the DPRK’s weapons buildup.
North Korea nuclear threat to Israel and Saudi Arabia
North Korea has miniaturized nuclear bombs, it is able to sell Iran ready-made bombs. Iran having nuclear weapons would be a threat to Israel and to Saudi Arabia.
North Korea helping Iran or selling Iran nuclear weapons would pose an existential threat to Israel.