U.S. President Barack Obama on Thursday issued his first direct call for Syrian President Bashar al-Assad to step down.

Obama said Assad must go "for the sake of the Syrian people."

Prime Minister Stephen Harper echoed Obama's demand that the Syrian leader must leave power immediately. European leaders also issued similar calls.

"The Assad regime has lost all legitimacy by killing its own people to stay in power," Harper said in a written statement.

International pressure against Assad is mounting after his continued attempts to violently crush a six-month uprising. Nearly 2,000 people are believed to have been killed in the crackdown, while tens of thousands have been arrested.

"It is clear that President Assad believes that he can silence the voices of his people by resorting to the repressive tactics of the past," Obama said. "But he is wrong. As we have learned these last several months, sometimes the way things have been is not the way that they will be.

"It is time for the Syrian people to determine their own destiny, and we will continue to stand firmly on their side."

P.O.V.: Should Syria's president resign, as Obama suggests? Take our survey.

Shortly after Obama issued his statement, U.S. Secretary of State Hillary Clinton said the move "will further tighten the circle of isolation around the [Syrian] regime."

"The people of Syria deserve a government that respects their dignity, protects theirs rights and lives up to their aspirations. Assad is standing in their way."

Britain, France and Germany also issued a statement calling for Assad to step down.

The Syrian president has told the United Nations that all military operations against protesters have come to a halt, a UN spokesman said earlier Thursday. However, activists say nine more people have been killed in the central city of Homs.

The calls for Assad to step down came the same day a UN human rights team said Syrian forces may have committed crimes against humanity.

The human rights investigators' report calls for the UN Security Council to refer Syria to the International Criminal Court.

"The mission found a pattern of human rights violations that constitutes widespread or systematic attacks against the civilian population, which may amount to crimes against humanity," the investigators said in their 22-page report.

Syria's representative to the UN said the U.S. is launching a diplomatic war against his country.

The UN Security Council emerged from a meeting Thursday afternoon saying it will start drafting a resolution to impose more sanctions on the Assad regime.

Philip Parham, the U.K.'s deputy ambassador to the UN, told reporters after the meeting that "the time has come for the council to take further actions to step up the pressure against those who are responsible for the violence against the citizens of Syria."

U.S. issues new sanctions

Obama said he has signed an executive order freezing all Syrian assets in the U.S. The order also banned the U.S. import of petroleum and petroleum products of Syrian origin.

Asked whether Canada will follow the American example and whether it would affect Canadian companies operating in the country, Foreign Affairs Minister John Baird said he's instructed his officials to look at the U.S. measures.

"But everything we do, we want to target the Syrian regime itself and we don't want to hurt the Syrian people. That's important. So we're looking at it all right now," Baird said.

Suncor, a Calgary-based energy company, operates a $1.2-billion natural gas project that is used to generate electricity for consumption in Syria. The project is co-owned by the Syrian state-owned General Petroleum Corp.

Kelli Stevens, a Suncor spokeswoman, said the company is reviewing the U.S. sanctions. She said the company is still able to produce natural gas in Syria under the current Canadian sanctions.

Stevens said Suncor has ethics policies in place and intends to keep complying with all sanctions.

"If Canada's already got economic sanctions and yet does nothing about Suncor, then it's just empty words," NDP defence critic Jack Harris said Thursday on CBC's Power & Politics with Evan Solomon, noting later that his comments were targeting the government, not the company.

Chris Alexander, parliamentary secretary to the minister of national defence, said economic sanctions are not enough on their own.

"They may be one of the elements," he said. "We want to do it in a co-ordinated way. We want it to have an impact that helps the Syrian people."