U.S. official Susan Rice called the Syrian Government report blaming terrorists for the massacre in Houla “another blatant lie,” according to CNN.com.

The Syrian government has blamed terrorists throughout the 15 months of violence, but Rice said there is “no factual evidence” to “substantiate that rendition of events.”

According to NPR, Rice said the best solution for Syria is a political one, as she said the U.S. government view has always been to resist increasing military involvement in Syria. She said they don’t want a proxy war to begin, as it would result in destruction for the region.

U.S. Defense Secretary Leon Panetta said Syrian President Bashar al-Assad must be removed from power for the violence to stop, according to CNN.

"There is no question that we are very concerned about the atrocities that are taking place in Syria," he said.

Investigators believed that armed men in military clothing attacked and executed families in Houla, and Rice said these men were militia fighting for the regime, according to CNN.

"They should also ask, frankly who are they arming inside of the Syrian opposition? You know and we know it is not a unified opposition. It's fragmented,” Rice said.

According to NPR, a briefing by Rice on Thursday indicated that if the Annan peace plan fails, the situation in Syria could turn into a civil war. 

"Just makes clear how important it is to remove Assad from power and to try to implement the necessary political reforms that are necessary in that country," Panetta said.