The U.S. government faced mounting calls for action against Libya on Tuesday as the regime of Muammar Gaddafi used tanks, helicopters and warplanes to unleash fresh attacks on pro-democracy demonstrators.

The White House said it offered condolences for victims of appalling violence and urged the Libyan government to respect the rights of its citizens.

Washington wants to work with the international community to talk with one voice on Libya, it said, and Secretary of State Hillary Clinton will speak later on Tuesday about the situation in the oil-producing North African country.

Senator John Kerry, the influential chairman of the Senate Foreign Relations Committee, called on the Obama administration to consider reimposing sanctions against Tripoli and said oil companies should cease operations in Libya immediately.

We're not without options, particularly in partnership with the broader international community, Kerry said in a statement that suggested Libyan commanders who participate in the crackdown could face international war crimes charges.

Kerry, who has the power to scrutinize U.S. foreign policy, said the Gaddafi government's use of deadly force against its own people should mean the end of the regime itself.

Former U.S. President George W. Bush removed a wide range of economic sanctions against Libya after its 2003 decision to give up its weapons of mass destruction programs and moved to settle claims stemming from the 1988 Lockerbie bombing.

Clinton has previously condemned the violence and called on the Libyan government to respect the rights of its people.

But critics have said the Obama administration should come down in favor of demonstrators and take steps to foil a Libyan communications blackout that is isolating protesters from the outside world.

Libya's ambassador to the United States, Ali Aujali, resigned as Tripoli's representative and urged Washington to step up its rhetoric at the U.N. Security Council, saying the time has come to topple Gaddafi's regime.

I need the United States to raise their voice very strongly. This regime is shaking and this is the time to get rid of it, Aujali said on ABC's Good Morning America.

Please, please, help the Libyan people. Help them. They are burning, he added. We need the world to stand up by us.

Kerry urged the U.N. Security Council to condemn the violence and explore temporary sanctions at an emergency session set for later on Tuesday.

The situation in Libya presents the Arab League and African Union with a chance to create a precedent in its response to the crisis, Kerry said.

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, he said.

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