(CNN) US Ambassador to the United Nations Nikki Haley addressed the Security Council Wednesday on the consequences of failing to act in response to chemical weapons attacks in Syria, as President Donald Trump considers whether and when to pull US troops out of the war-torn country.

"It is a sad fact that, just a few years ago, a single chemical weapons attack would have united us in shock and anger," said Haley. "It would have been enough for us to take immediate action. Now, we have a regime that uses chemical weapons practically every other week."

Haley's remarks come exactly one year after the sarin gas attack killed over 80 people in the Syrian town of Khan Sheikhoun, prompting Trump to strike a Syrian government air base with Tomahawk cruise missiles.

Yet on Tuesday, Trump suggested at a news conference he wanted to remove US troops from Syria -- a move he says reflects progress in the US mission to confront the terror group ISIS, but critics say would further embolden the Assad regime and its main allies, Russia and Iran.

And while Trump privately told his national security team he was willing to keep troops there in the short-term, he made it clear he doesn't want them in Syria for the long-term and expects the costs of stabilizing Syria to be shouldered by regional players.

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