Prime Minister Stephen Harper called on Syria's ruler to resign on Thursday, joining world leaders who are using tough talk and sanctions to pressure President Bashar Assad to stop attacking his own people.

"Canada reiterates its strong condemnation of the ongoing violent military assault by the Assad regime against the Syrian people. This campaign of terror must stop," Harper said in a statement.

"The Assad regime has lost all legitimacy by killing its own people to stay in power."

Hundreds of Syrians have been killed since the start of August as Assad's regime unleashed tanks, ground troops and snipers against those protesting against the country's governing regime.

U.S. President Barack Obama and European leaders have also called for Assad to step down and spare his people from the brutal repression they experience under his regime.

In a stinging written statement released Thursday, Obama said Assad has overseen an assault on Syrian people as they protest for freedom. Obama said the Syrian people will decide their country's future once Assad no longer stands in the way.

"For the sake of the Syrian people, the time has come for President Assad to step aside," Obama said in a statement. "The Syrian government has insisted the crackdown is targeting terrorists attempting to create unrest and has lashed out at the international community for interfering."

The U.S. and Canada also said on Thursday that they have imposed diplomatic sanctions against Syria until Assad vacates his position.

The sanctions are designed "to target the Syrian regime itself," rather than the country's population, Foreign Affairs Minister John Baird said during a news conference Thursday afternoon.

Canada is calling on "like-minded partners" to set up a co-ordinated set of sanctions against the Assad regime, he added.

When asked what action will be taken if Assad refuses to step down, Baird replied that Ottawa will "keep up the diplomatic efforts in support of the Syrian people."

According to human rights groups, Assad's forces have killed close to 2,000 people since mass protests broke out in mid-March and the attacks have increased since Ramadan began earlier this month.

Germany, France, Britain and Belgium also asked Assad to step down Thursday, further isolating an oppressive regime that has ruled Syria for four decades.

A UN report released Thursday also recommended that Syria be referred to the International Criminal Court for allegedly committing crimes against humanity. For instance, Syria is accused of targeting children during violent crackdowns against demonstrations.

Experts doubt impact of sanctions

But with little appetite for another military intervention among members of the international community, questions remain about how the violence in Syria will end if Assad doesn't buckle under the diplomatic pressure.

"We've seen situations like this before," said Christopher Sands, with the Hudson Institute in Washington.

"When a leader is really digging in as Bashar Assad appears to be doing -- willing to kill large numbers of his own people -- he's crossed a line that I think to some extent makes him immune or unwilling to respond to these international gestures," he told CTV News Channel on Thursday.

"The only thing that will turn him around is either his success, or his ultimately being deposed by his own people."

With files from The Associated Press