The White House has added its voice among international leaders to come out in condmenation of an attack in Syria that killed at least 90 people, including 32 children.
Erin Pelton, spokeswoman for the National Security Council called the attack a "vile testament to an illegimate regime" on Saturday.
Washington said the government of Bashar al-Assad, the Syrian president, is responding to peaceful political protest with "unspeakable and inhuman brutality".
Hillary Clinton, the US secretary of state, said in a separate statement that "the United States will work with the international community to intensify our pressure on Assad and his cronies, whose rule by murder and fear must come to an end".
The attack, captured in over a dozen amateur online videos, also sparked outrage from the United Nations.
"This appalling and brutal crime involving indiscriminate and disproportionate use of force is a flagrant violation of international law and of the commitments of the Syrian government to cease the use of heavy weapons in population centers and violence in all its forms", said Ban Ki-Moon, the UN secretary general, and Kofi Annan, the joint UN-Arab League envoy to Syria.
"Those responsible for perpetrating this crime must be held to account" said Annan.
The attack has called the effectiveness of a joint UN-Arab League brokered ceasefire into further question.
William Hague, the British foreign secretary, said in a statement "we are consulting urgently with our allies on a strong international response, including at the UN Security Council, the EU and UN human rights bodies".
London would seek an urgent session of the Security Council in coming days, in response to "credible and horrific reports that a large number of civilians have been massacred" by Syrian forces in Houla.
Hague also called for "full and immediate access" to the group of villages northwest of the besieged city of Homs.
France said it was making plans to host a "Friends of Syria" meeting in the wake of the latest deadly violence.
"I condemn the atrocities committed daily by Bashar al-Assad on his own people," Laurent Fabius, the new French foreign minister, said.
"With these new crimes his murderous regime plunges Syria further into horror and threatens regional stability."
German Foreign Minister Guido Westerwelle said he was "shocked and horrified" at the killings.
"It is appalling that the Syrian regime does not put an end to the brutal violence against its own people," Westerwelle said in a statement. "Those responsible for this crime must be punished."
The London-based Syrian Observatory for Human Rights released an unusually harsh statement, calling Arab nations and the international community "partners" in the killing "because of their silence about the massacres that the Syrian regime has committed".