Author Gordon Chang said Friday that North Korean dictator Kim Jong Un was "unnerved" by the Syrian airstrikes President Donald Trump ordered last week, most likely leading to his announcement to suspend Pyongyang's nuclear and ballistic missiles tests.

"What President Trump did in the Syrian raid was say: 'Thou shalt not use chemical weapons,'" Chang, a longtime expert on North Korea, told David Asman on Fox Business.

"We've got to remember that Kim last year used chemical weapons on his half-brother."

Kim's half-brother, Kim Jong Nam, was killed in a February 2017 attack at a Malaysian airport by two unidentified women with "poisoned needles," according to news reports.

He complained to staff at Kuala Lumpur International Airport that his face had been sprayed while he was preparing for a flight to Macau.

Kim had $138,000 in cash in his backpack at the time of the attack.

In his Friday announcement, Kim Jong Un also said that North Korea would close its atomic testing site in a move that followed a secret meeting with CIA Director Mike Pompeo in Pyongyang over Easter.

Both Trump and Vice President Mike Pence took to Twitter to praise Kim's decision:

Trump and Kim now are expected to meet in late May or June.

In last week's airstrikes, U.S. and forces from France and Britain fired 105 missiles on three Syrian targets in or near Damascus that developed, tested or stored chemical weapons.

The offensive came in response to President Bashar al-Assad's use of chlorine gas in an April 7 attack that killed as many as 70 people and injured 1,000 others.

In his Fox Business interview, Chang said that Pyongyang has played an active part in Syria's chemical weapons activities since the mid-1990s.

"The other connection here is that North Korea is the primary supplier to Syria of chemical weapons," he told Asman. "They've had this chemical-weapons relationship since the mid-1990s.

"There are two Syrian chemical facilities that the North Koreans built.

"North Koreans have been killed in Syria in connection with chemical-weapons events," Chang said.

"Kim certainly, I think, was unnerved by what happened last week."