Syrian activists say President Bashar al-Assad's government is continuing its crackdown on protesters, despite U.S. and European demands that he step down.

Activists say Syrian security forces opened fire in the central city of Homs Thursday night, killing at least one person. More shooting was heard Friday in Homs, where protest organizers have called for more demonstrations.

The reports of continuing violence come after Mr. Assad told United Nations Secretary General Ban Ki-moon Wednesday that military and police operations had stopped.

The U.S. estimates the Assad government is responsible for more than 2,000 deaths since protests against his rule began in March. On Thursday, U.S. President Barack Obama issued his first direct call for Mr. Assad to leave power, saying the Syrian leader's calls for dialogue and reform have “rung hollow” while he is “imprisoning, torturing, and slaughtering his own people.”

The European Union, Britain, France, Germany and Canada also urged Mr. Assad to step down, with EU foreign policy chief Catherine Ashton saying he has completely lost legitimacy. She said the EU is preparing to broaden its sanctions against Syria.

Mr. Obama also announced new sanctions against the Assad government, ordering Syrian government assets in the U.S. frozen, prohibiting U.S. citizens from operating in or investing in Syria and banning U.S. imports of Syrian oil products.

In New York, the U.S. and four European members of the United Nations Security Council said they would begin drafting a U.N. sanctions resolution against Syria. But it could be a lengthy and difficult process to persuade council members Russia and China not to veto such a measure.

Syria's U.N. ambassador, Bashar Ja'afari, accused Washington and some other Security Council members of waging what he called a “diplomatic and humanitarian war” against his country.

In a report released Thursday, the U.N. human rights office said Mr. Assad's forces have carried out widespread and systematic attacks on civilians that “may amount to crimes against humanity.” The report said the victims' wounds were consistent with a “shoot to kill policy.”

U.N. human rights chief Navi Pillay told the Security Council it should refer the situation in Syria to the Hague-based International Criminal Court. The world body plans to send a team to Syria in a few days to assess the humanitarian situation there.