President Barack Obama called Thursday for Syrian leader Bashar al-Assad to step down — significantly ratcheting up international pressure against a regime that has been criticized for its harsh crackdown against anti-government protesters in recent months.

“The future of Syria must be determined by its people, but President Bashar al-Assad is standing in their way,” Obama said in a written statement. “We have consistently said that President Assad must lead a democratic transition or get out of the way. He has not led. For the sake of the Syrian people, the time has come for President Assad to step aside.”

U.S. authorities also imposed new economic sanctions against Damascus, freezing Syrian government assets in the United States, barring Americans from making new investments in Syria and prohibiting any U.S. transactions relating to Syrian petroleum products, among other things.

Obama administration officials previously said al-Assad has “lost legitimacy” and that Syria “would be better off” without him. Until now, however, U.S. authorities had resisted calling explicitly for his ouster.

The public call for al-Assad’s to step down — long awaited in many quarters — was closely coordinated with European, Turkish and Arab allies. It came one day after al-Assad told the head of the United Nations that military and police operations against anti-government protesters have stopped, according to a statement released by the U.N. secretary-general’s office.

READ MORE: CNN