President Trump said Thursday that the U.S. has killed more Islamic State extremists in the Middle East under his brief leadership than during eight years under President Barack Obama.

“ISIS is rapidly disappearing, as you know,” Mr. Trump said in a news conference with the Emir of Kuwait. “What we do is we kill ISIS, and we have succeeded in that respect. That’s because of our great military. We have done better in the previous eight months of my presidency than we did in the previous eight years against ISIS.”

The Islamic State formed officially in 2014, and quickly overran large parts of Syria and Iraq to create its so-called “caliphate.” Mr. Trump has blamed Mr. Obama for creating the conditions that led to the extremist group by withdrawing U.S. forces from Iraq in 2011.

Asked if Syrian President Bashar al Assad is using chemical weapons again in that country’s civil war, Mr. Trump said he would be “extremely upset” if that were the case. Mr. Trump ordered missile strikes against the Syrian military last spring in response to a chemical weapon attack against civilians.