WASHINGTON (AP) -- President Barack Obama on Friday declared the U.S. and its allies would consider "every tool available" to stop the slaughter of innocent people in Syria, using his most forceful words to date in response to an increasingly grim crisis that has gripped the world.
The president did not give specifics about what the U.S. or other countries would do to help.
"It is absolutely imperative for the international community to rally and send a clear message to President (Bashar) Assad that it is time for a transition," Obama said after a meeting with the Danish prime minister. "It is time for that regime to move on. And it is time to stop the killing of Syrian citizens by their own government."
The president added that nations cannot afford to be "bystanders" as the killing continues.
Obama spoke shortly after Secretary of State Hillary Rodham Clinton used strong language to denounce Russia and China for protecting Syria, and the president's language about the need for world unity was viewed as a similar condemnation of those two nations.
Obama said he was encouraged by developments out of Tunisia on Friday, where more than 60 nations, in a unified bloc, asked the United Nations to begin planning a civilian peacekeeping mission that would deploy after the Assad regime halts its brutal crackdown on the opposition.
The Tunisia meeting is the latest international effort to end the crisis, which began when protesters inspired by uprisings sweeping across the Arab world took the streets in some of Syria's impoverished provinces nearly a year ago to call for political change.
Assad's security forces have responded with a fierce crackdown. There is no end in sight.
The government blames the violence on Islamic extremists and armed gangs. The situation has grown increasingly militarized in recent months, with opposition forces increasingly taken up arms against the regime. The U.N. estimated in January that 5,400 people were killed in the conflict in 2011. Hundreds more have died since.
Obama's language was stronger than in the past, reflecting the worsening humanitarian crisis and the urgent efforts to help civilians in the short run.
Among the near-term options to help civilians are Red Cross evacuation missions like one that brought at least seven wounded people out of Homs on Friday, and larger international efforts to get humanitarian supplies into the country. The Obama administration has not called for any specific action but would almost certainly be part of any large-scale humanitarian relief effort that might be organized over the coming days or weeks.
A broad humanitarian relief effort would require agreement from the Assad government, perhaps under a negotiated cease-fire.
Assad has not indicated he is willing to broker any deal.
And unlike in Libya last year, there is no international consensus for a military confrontation with Syria.
The U.S. and European allies had sought a resolution at the U.N. Security Council that would have backed an Arab League plan for Assad to leave power, but the measure was blocked by both Russia and China.
Clinton, speaking at the Tunisia meeting Friday, blasted both countries for opposing U.N. action, calling it "despicable." Clinton said she would be willing to go back to the U.N. as often as needed, "but we need to change the attitude of the Russian and Chinese governments."
Obama spoke following an Oval Office meeting with Danish Prime Minister Helle Thorning-Schmidt. The prime minister said the situation in Syria is "horrendous" and urged the international community to keep up the pressure on Assad's regime.
Said Obama: "We are going to continue to keep the pressure up and look for every tool available to prevent the slaughter of innocents in Syria." He said he and the prime minister agreed that it is vital "that we not be bystanders during these extraordinary events."
Associated Press writers Anne Gearan and Julie Pace contributed to this report.