The aircraft targeted al-Brega and Ajdabiya, both of which were hit with bombs on March 1.

Opposition forces said they were forging ahead, working to maintain their positions and fend off attacks by pro-Gadhafi forces. Rebels have armed themselves in some cases by raiding military installations and police stations.

Morale on the part of the opposition seems to be high, while morale among Gadhafi's forces - which have seen defections as some members of the military have joined the protests - seems low.

Libyan jets on Thursday dropped two bombs over al-Brega - one near a military checkpoint and one near the main gate to a refinery, witnesses reported.

In Ajdabiya,a tribal leader said the military dropped two bombs on military camps.

The situation in Libya is different from those in neighboring Tunisia and Egypt, where uprisings turned into revolutions that overthrew their rulers. Libya is facing a battle between government forces and rebel forces. "This is becoming a war," Wedeman tweeted.

The more Libyan leader Moammar Gadhafi uses aerial attacks, the more pressing discussions become in the West about imposing a no-fly zone over the country.

US military and diplomatic officials - including Defense Secretary Robert Gates, Chairman of the Joint Chiefs of Staff Adm. Michael Mullen and Secretary of State Hillary Clinton - have all said enacting a no-fly zone is complicated and risky, and international support for the idea is not there yet.

The UN refugee agency reported that nearly 150,000 people had crossed Libya's borders into Egypt and Tunisia, and thousands more were arriving hourly at the borders.

US President Barack Obama said he approved the use of US military aircraft to help return to Egypt those Egyptian citizens who have fled to Tunisia to escape the unrest in Libya. He said he has also authorized the US Agency for International Development to charter civilian aircraft to help people from other countries get back home.