"I highly valued President Trump's strong commitment to the maintenance of the worldwide order and to the peace and security of its allies and the world", Abe told reporters after the talks.
"The number one threat in the region continues to be North Korea due to its reckless, irresponsible and destabilizing program of missile tests and pursuit of a nuclear weapons capability", U.S. Pacific Command spokesman Dave Benham told reporters.
The airstrikes, announced shortly after Trump and Chinese President Xi Jinping wrapped up dinner at a two-day summit in Florida last week, were retaliation against Syrian President Bashar Assad for a chemical weapons attack against civilians caught up in his country's long civil war.
"It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons", Trump said in a brief televised address about an hour after the strike was launched. The Syrian government denied carrying out the chemical attack. At that time, Trump told Abe that the United States considers that all options are on the table in dealing with the North.
He closed the letter with the following statement: "The United States will take additional action, as necessary and appropriate, to further its important national interests".
At closer range, Japan has been rattled by North Korea's repeated recent test-firings of short- and medium-range ballistic missiles in its direction, the latest just two days before Trump sat down with Xi.
"Some forces are loud-mouthed that the recent USA military attack on Syria is an action of warning us but we are not frightened by it", the report said, adding that the North's "tremendous military muscle with a nuclear force as its pivot" will foil any aggression by the U.S. But unlike Syria, experts warn that North Korea has a means of striking back if provoked.
The attack was the first direct US assault on Syria and the government of President Bashar al-Assad in the six-year war there.
The former senior vice foreign minister also said the USA missile attack on Syria could cut both ways - it could work as a deterrent toward the North or it could push Pyongyang into a corner.