The Observatory said a rebel commander, who headed the Two Shrines Brigade, was killed in the fighting around the base. It added that six government troops were also killed in the clashes.
In the southern province of Daraa, also known as the Houran plains, the Observatory and the LCC said rebels had launched a new offensive called "the Houran Volcano" in which they are targeting army checkpoints and positions.
The Observatory said there were an unknown number of casualties on both sides.
An amateur video posted online showed rebel artillery fire hitting al-Khudr military base, located on a hill near the town of Dael, also in the province. The crackle of gunfire could be heard in the distance.
The video appeared genuine and corresponded to other AP reporting on the events depicted.
The Observatory reported shelling and clashes in other areas, including Damascus and its suburbs as well as the central province of Homs and Deir el-Zour to the east that borders Iraq.
Syria's conflict started with largely peaceful anti-government protests in March 2011 but eventually turned into a civil war. More than 70,000 people have been killed, according to the United Nations.
The New York-based Human Rights Watch said Saturday that recent Syrian government air and missile strikes have caused civilian casualties in opposition-held areas in Aleppo province "in violation of the laws of war." It said the attacks left at least 84 people dead.
The rights group said its team in the province, which investigated recent attacks, said dozens of civilian homes also had been destroyed "without damaging any apparent opposition military targets."
During a recent seven-day mission to Aleppo, Human Rights Watch researchers documented five attacks between March 18 and April 7. It said that of the 84 killed in these attacks, 36 were children.
"In all the new cases, witnesses told Human Rights Watch that the only people killed or injured by the strikes had been civilians, and that only civilian buildings had been hit," the group said.
"In attack after attack in Aleppo, it is only civilians and civilian homes that are hit by government airstrikes," said Anna Neistat, associate program and emergencies director at Human Rights Watch. "The Syrian Air Force knows very well that using cluster bombs and raining down missiles and bombs indiscriminately on urban areas violates the laws of war."