President Barack Obama for the first time called on Syrian President Bashar al-Assad to leave office, saying “the time has come” for the Syrian people to determine their future.

The explicit demand for Assad’s departure comes more than a month after Obama said Assad had lost legitimacy to lead and as momentum builds at the United Nations for a formal resolution against the bloodshed. Turkish Foreign Minister Ahmet Davutoglu said on Aug. 15 that “time for words will be over” unless Syria ends military operations against its people.

Obama also signed an executive order freezing any Syrian government assets in the U.S. and banning import to the U.S. of petroleum products of Syrian origin. The order denies Syria access to the U.S. financial system and prohibits people in the U.S. from doing business with Syria, according to a Treasury Department statement.

“The order strikes at a crucial revenue stream for Syria’s government” and will disrupt the Assad regime’s “ability to finance its campaign of violence against the Syrian people,” Treasury Secretary Timothy Geithner said in the statement.

Human-rights activists who have compiled names of the dead since the uprising began five months ago say Syrian forces have slaughtered more than 2,400 anti-government demonstrators.

Pressure has been mounting this month for bolder steps against Assad after Saudi Arabia, Kuwait, Bahrain and Tunisia withdrew their ambassadors from Damascus. In Washington, the Treasury Department last week extended sanctions against Assad and his closest collaborators even though Syria is an economy the U.S. has little influence on.

The Syrian government’s crackdown on dissent is so deadly that it merits investigation by the International Criminal Court, the United Nations High Commissioner for Human Rights is prepared to tell the Security Council today. There is evidence Syria has violated international law, said a UN diplomat briefed on the findings who wasn’t authorized to discuss them publicly.

The UN report combined with Obama’s tougher language should lead to a renewed European-led push at the UN to overcome Russian opposition and put a resolution to the vote.

Criticism by Arab nations has left Assad increasingly isolated, leaving Iran as his only unwavering ally left in the region. Even Lebanon, part of the UN Security Council, didn’t block a statement from the 15-member body that condemned the use of force in five months of violence.

The Obama administration has slowly been adopting sterner language against Assad, culminating in today’s expected action. On July 12, Obama told CBS that “increasingly you’re seeing President Assad lose legitimacy in the eyes of his people.”