BREGA, LIBYA - Forces loyal to Libyan leader Moammar Gaddafi launched renewed airstrikes against two key rebel-held towns Thursday, a day after poorly armed citizens repelled a major government assault on the area.

In Washington, President Obama issued his strongest condemnation of Gaddafi to date and announced he was sending U.S. military planes to help repatriate Egyptians who have fled to the Tunisian border.

He did not rule out imposing a "no-fly zone" over Libya to ground Gaddafi's air force, saying that was "one of the options" he has asked his administration to explore. But he stressed that any such decision needs to be made in consultation with NATO and the international community.

"We will continue to send a clear message: the violence must stop," Obama said in opening remarks at a White House news conference with visiting Mexican President Felipe Calderon. "Moammar Gaddafi has lost legitimacy to lead, and he must leave. . . . The aspirations of the Libyan people for freedom, democracy and dignity must be met." Obama previously had called for Gaddafi's departure from power in a written statement.

In response to questions, Obama warned that Gaddafi's supporters will be held accountable for violence they perpetrate against civilians. "They should know that history is moving against Colonel Gaddafi," he said.

Obama spoke after Brega, a key oil port, was hit Thursday morning by at least three powerful airstrikes. There was also a strike near an army munitions storage unit just outside Ajdabiya, about 40 miles away. No casualties were reported in the airstrikes.

About 28 miles west of Brega, rebels clashed with Gaddafi loyalists Thursday in the Mediterranean coastal town of Bishra. Truckloads of rebel fighters left Benghazi to help their allies in Bishra. Details of the fighting there were not immediately available.

In The Hague, the chief prosecutor for the International Criminal Court told reporters he would investigate Gaddafi and his inner circle for alleged crimes against humanity.

Luis Moreno-Ocampo vowed there would be "no impunity in Libya" and said he was contacting former Libyan officials and army officers to determine who would have ordered alleged attacks on peaceful demonstrators, the Associated Press reported. He said he is seeking video and photographic evidence of any alleged atrocities.

"We are not saying who is responsible yet," Moreno-Ocampo said. "Today is the start of the investigation."

Also Thursday, officials said a Dutch helicopter crew attempting to evacuate people from Libya had been captured over the weekend by forces loyal to Gaddafi. The three marines and their helicopter are still being held by Libyan authorities, a Dutch Defense Ministry spokesman told the Associated Press. He said officials are in "intensive negotiations" to secure their release.

On Wednesday - despite aged equipment and little training - a ragtag team of thousands of Libyan rebels rushed to Brega and drove back government forces, retaking the port city after setbacks earlier in the day.