President Barack Obama emphasized his deep concern about the Syrian government's use of violence against civilians in a phone call Thursday with Turkish Prime Minister Tayyip Erdogan, the White House said.

The two leaders agreed that the bloodshed must immediately end, the White House said. Separately, presidential spokesman Jay Carney stopped just short of calling for President Bashar Assad's ouster, saying that Syria "would be a much better place without him."

"We believe that President Assad's opportunity to lead the transition has passed," Carney told reporters traveling on Air Force One with Obama to Michigan.

The developments came as violence escalated against demonstrators in Syria and as the Obama administration, which announced new sanctions against Syria Wednesday, appeared to move closer to calling directly for Assad to step down.

The White House said Obama and Erdogan also agreed that the demands of the Syrian people for a transition to democracy must be met, and that the pair agreed to consult closely in the coming days as the situation in Syria develops.

A series of foreign diplomats have traveled to Damascus urging Assad to end a campaign of killing. Turkey's foreign minister was among those who have met with Assad. And on Thursday, Robert Ford, the U.S.¬ambassador to Syria, met with Syrian Foreign Minister Walid Muallem in Damascus.

State Department spokeswoman Victoria Nuland said Ford made clear "that Syria is going to face increasing pressure if the violence doesn't end" and that empty rhetoric wouldn't satisfy demands for reforms.

Ford "challenged the regime's lip service about enacting reform, and he called for free and open access for the media," Nuland told reporters.

She said Ford also demanded strict adherence from Syrian authorities with their obligations to protect diplomatic personnel. Pro-government protesters stormed the U.S. Embassy in Damascus in July.