The Obama administration on Thursday called for Syrian President Bashar Assad to step down.
The White House issued a statement demanding Assad leave power and warned of "unprecedented sanctions" against the regime.
The Syrian people "have spoken with their peaceful marches, their silent shaming of the Syrian regime, and their courageous persistence in the face of brutality - day after day, week after week," President Obama said.
"The Syrian government has responded with a sustained onslaught. I strongly condemn this brutality," he added.
Secretary of State Hillary Rodham Clinton will also make a televised statement to reinforce the U.S. position, the officials said.
Many European nations are expected to follow the United States' lead.
Clinton on Tuesday publicly questioned the effectiveness of the United States acting alone.
"It is not going to be any news if the United States says Assad needs to go," she said. "OK, fine, what's next? If other people say it, if Turkey says it, if King Abdullah says it, there is no way the Assad regime can ignore it."
It is hoped such an announcement would send a powerful signal that Assad is no longer welcome in the international community. The additional sanctions would further boost pressure on Assad and his inner circle.
Syrian security and military forces are accused of killing more than 1,800 peaceful protestors since March.
A United Nations human rights team says the actions may, "amount to crimes against humanity" and should be brought to the International Criminal Court.
President Barack Obama, Clinton and top national security aides have previously said that Assad has "lost his legitimacy" as a leader and that Syria would be "better off" without him. But they had not specifically demanded that he step down.
Thursday's expected new formulation of policy will make it clear that Assad can no longer be a credible reformist and has to leave, the officials said.