"Everyone is going to feel it at this point," Haley said, warning of consequences for Assad's foreign allies.

WASHINGTON (AP) — President Donald Trump on Sunday defended his use of the phrase "Mission Accomplished" to describe a U.S.-led missile attack on Syria's chemical weapons program, even as his aides stressed continuing U.S. troop involvement and plans for new economic sanctions against Russia for enabling the government of Bashar Assad.

Stepping up the pressure on Syria's president, U.S. Ambassador Nikki Haley indicated the sanctions to be announced Monday would be aimed at sending a message to Russia, which she said has blocked six attempts by the U.N. Security Council to make it easier to investigate the use of chemical weapons.

"Everyone is going to feel it at this point," Haley said, warning of consequences for Assad's foreign allies.

"The international community will not allow chemical weapons to come back into our everyday life," she said. "The fact he was making this more normal and that Russia was covering this up, all that has got to stop."

Trump tweeted Sunday that the strike was "perfectly carried out" and that "the only way the Fake News Media could demean was by my use of the term "Mission Accomplished."" He added that he knew the media would "seize" on the phrase, but said it should be used often. "It is such a great Military term, it should be brought back," he wrote.

Trump tweeted "Mission Accomplished" on Saturday after U.S., French and British warplanes and ships launched more than 100 missiles nearly unopposed by Syrian air defenses. While he declared success, the Pentagon said the pummeling of three chemical-related facilities left enough others intact to enable the Assad government to use banned weapons against civilians if it chooses.

His choice of words recalled a similar claim associated with President George W. Bush following the U.S.-led invasion of Iraq. Bush addressed sailors aboard a Navy ship in May 2003 alongside a "Mission Accomplished" banner, just weeks before it became apparent that Iraqis had organized an insurgency that would tie down U.S. forces for years.

Later Sunday, Trump sent a letter to congressional leaders informing them in writing of his decision to order the strike. Under the War Powers Resolution, the president must keep Congress informed of such actions.

Haley made clear the United States won't be pulling troops out of Syria right away, saying U.S. involvement there "is not done."

Haley said the three U.S. goals for accomplishing its mission are making sure chemical weapons are not used in a way that could harm U.S. national interests, defeating the Islamic State group and having a good vantage point to watch what Iran is doing.

"We're not going to leave until we know we've accomplished those things," she said.

Haley said the joint military strike "put a heavy blow into their chemical weapons program, setting them back years" and reiterated that if Assad uses poison gas again, "the United States is locked and loaded."

French President Emmanuel Macron said Sunday that France wants to launch a diplomatic initiative over Syria that would include Western powers, Russia and Turkey. Speaking on French television BFM and online site Mediapart, Macron stressed that the French diplomacy is able to talk with Iran, Russia and Turkey on one side and to the United States on the other side.

He said, "Ten days ago, President Trump wanted to withdraw from Syria. We convinced him to remain."

The nighttime assault on Syria was carefully limited to minimize civilian casualties and avoid direct conflict with Russia, but confusion arose over the extent to which Washington warned Moscow in advance. The Pentagon said it gave no explicit warning. The U.S. ambassador in Moscow, John Huntsman, said in a video, "Before we took action, the United States communicated with" Russia to "reduce the danger of any Russian or civilian casualties."

Russia has military forces, including air defenses, in several areas of Syria to support Assad in his long war against anti-government rebels.

Russia and Iran called the use of force by the United States and its French and British allies a "military crime" and "act of aggression." The U.N. Security Council rejected a Russian resolution calling for condemnation of the "aggression" by the three Western allies.