"We offer our condolences to families of the victims in Libya of this appalling violence," Carney told reporters traveling with President Barack Obama to Cleveland.
Meanwhile, top lawmakers said the U.S. should consider imposing new sanctions on the regime and called for foreign energy companies to immediately shut down operations in the oil-rich North African nation.
Sen. John Kerry, chairman of the Senate Foreign Relations Committee, said in a statement that the violent crackdown was "cowardly" and "beyond despicable." He urged U.S. and international oil companies to immediately suspend their Libyan operations until attacks on civilians stop.
He also called on the Obama administration to consider re-imposing sanctions against Libya that were lifted by President George W. Bush after Gadhafi renounced terrorism and abandoned development of chemical, biological and nuclear weapons. He said the Arab League and African Union should investigate reports of atrocities.
"These are concrete steps that must be taken now and in the days ahead to show that the world will respond with actions not just words when a regime wields reprehensible violence against its own people," said Kerry.
The White House has sometimes tapped Kerry to float possible foreign policy strategies. Asked about Kerry's suggestions, Carney said, "We are looking at his proposal but right now we are focusing on ending the bloodshed."
"The Libyan regime's widespread attacks on the Libyan people are deplorable, and all responsible for these attacks must be held to account," she said in a statement.
Gadhafi appeared on state television Tuesday and vowed to fight protesters and to die a martyr. Despite eyewitness accounts of soldiers, including alleged mercenaries, opening fire on protesters in numerous cities, he said he had not ordered the demonstrations suppressed with violence. But he said those agitating for change deserved the death penalty under Libyan law.