He had previously declared the end of ISIS in the Syrian region.
Washington: US President Donald Trump on Sunday (local time) slammed Russia, Syria and Iran for "killing many innocent civilians" by "bombing the hell out" of Idlib in Syria.
"Hearing word that Russia, Syria and, to a lesser extent, Iran, are bombing the hell out of Idlib Province in Syria, and indiscriminately killing many innocent civilians. The World is watching this butchery. What is the purpose, what will it get you? STOP!" he tweeted.
The US President was en route to the UK for his official visit.
He had previously declared the end of ISIS in the Syrian region, basing that as his reason behind the decision to pull troops from the area. This decision invited backlash from various quarters, including the US Congress, as it left the country's allies in a lurch.
Following this, the US authorities ensured that 400 troops, out of the 2,000-strong American contingent, would stay back in Syria. Many viewed the United States' withdrawal from the region as the direct growth of Russia and Iran's influence in Syria.