WASHINGTON — The U.S. is working with France and the U.K. on plans for a coordinated military strike in Syria if the regime uses chemical weapons in an expected offensive against the country’s last major rebel haven, President Donald Trump’s national security adviser said.

John Bolton warned Monday that a new attack by the Western allies would be much stronger than the two airstrikes launched in April 2017 and April 2018 after Syrian President Bashar al-Assad was accused of using chemical weapons that killed scores of civilians in the past 17 months.