The U.S., for the first time, called for Syrian President Bashar al-Assad to step down from power Thursday as it announced a new executive order imposing harsher sanctions on his regime.

President Barack Obama said in a statement that the Syrian people, thousands of whom have been killed while protesting for months for reforms, “have braved ferocious brutality at the hands of their government,” which “responded with a sustained onslaught.”

“For the sake of the Syrian people, the time has come for President Assad to step aside,” said Obama in the statement.

The sanctions announced Thursday freeze any assets of the Syrian government under U.S. jurisdiction and prohibit any U.S. person from operating or investing in Syria.