Updated

American warplanes, ships and submarines prepared to launch a furious assault on Libya's limited air defenses Saturday, clearing the way for European and other planes to enforce a no-fly zone designed to ground Moammar Gadahfi's air force and cripple his ability to inflict further violence on rebels, U.S. officials said.

Hours after Secretary of State Hillary Rodham Clinton attended an international conference in Paris that endorsed military action against Gadhafi, the U.S. was poised to kick off its attacks on Libyan air defense missile and radar sites along the Mediterranean coast to protect no-fly zone pilots from the threat of getting shot down.

A U.S. official, speaking on condition of anonymity in order to discuss sensitive military operations, said the Obama administration intended to limit its involvement — at least in the initial stages — to helping protect French and other air missions.

An attack against air defenses with Navy sea-launched Tomahawk cruise missiles was planned for later Saturday, one official said. The U.S. also has the ability to knock out air defense radars with Navy electronic warfare planes.

At a news conference in Paris, Clinton said Gadhafi had left the world no choice but to intervene urgently and forcefully to protect further loss of civilian life.

"We have every reason to fear that left unchecked Gadhafi would commit unspeakable atrocities," she told reporters.

Clinton said there was no evidence that Gadhafi's forces were respecting an alleged cease-fire they proclaimed and the time for action was now.

"Our assessment is that the aggressive action by Gadhafi's forces continues in many parts of the country," she said. "We have seen no real effort on the part of the Gadhafi forces to abide by a cease-fire."

President Barack Obama announced on Friday that he had given the go-ahead for U.S. forces to participate in operations designed to enforce the provisions of a U.N. Security Council resolution demanding that Gadhafi cease firing on civilians. At the outset of a visit to Brazil on Saturday, he spoke briefly about Libya, noting the Paris talks.

"Our consensus was strong and our resolve is clear," Obama said. "The people of Libya must be protected and in the absence of an immediate end to the violence against civilians our coalition is prepared to act and to act with urgency."

Among the U.S. Navy ships in the Mediterranean were two guided-missile destroyers, the USS Barry and USS Stout, as well as two amphibious warships, the USS Kearsarge and USS Ponce, and a command-and-control ship, the USS Mount Whitney. The submarine USS Providence was also in the Mediterranean.