WASHINGTON - The U.S. military on Saturday continued to launch four airstrikes against forces of Islamic State of Iraq and the Levant (ISIL) in Iraq, U.S. Department of Defense said via its official Twitter account.

This marks the third round of airstrikes against Islamic State forces by the U.S. military since they were authorized by President Barack Obama two days ago.

The first strike was carried out by a mix of U.S. fighters and remotely piloted aircraft at approximately 11:20 a.m. EDT, the U.S. Central Command said in a statement, adding that it destroyed an armored personnel carrier (APC) of ISIL that was firing on Yazidi civilians trapped on Mount Sinjar.

Twenty minutes later, U.S. aircraft launched two more strikes that destroyed two ISIL APCs and an armed truck nearby, the statement said.

At around 3:00 p.m. EDT, U.S. aircraft destroyed another APC in the area of Sinjar in a fourth strike, according to the U.S. central command.

U.S. warplanes also bombed several Islamist fighters in the first two rounds of strikes near the northern Iraqi city of Erbil on Friday.

Obama said earlier Saturday that the targeted airstrikes in Iraq could continue for some time, but refused to give a particular timetable, saying "I don't think we are going to solve this problem in weeks."

He warned that the new campaign to bring security in Iraq requires military and political changes and "is going to be a long-term project."

But he made clear that his administration would not send ground troops back to Iraq.