"The missiles, suspected to be Israeli, destroyed an arms warehouse near the Damascus worldwide airport", Observatory head Rami Abdel Rahman told AFP.
On Sunday, the monitoring group said that the alleged Israeli strike caused "substantial" damage at the airport, but had no immediate information on casualties.
In a shaky video, a small, bright explosion is seen in the night sky, with city lights in the distance.
According to the Al-Mayadeen TV channel, several blasts were heard in the vicinity of the airport.
The attack is the latest in a string of Israeli missile strikes that targeted Syrian military bases during the protracted war in the country.
"The missiles, suspected to be Israeli, destroyed an arms warehouse near the Damascus International Airport", Observatory head Rami Abdel Rahman told AFP.
Israel rarely acknowledges strikes inside Syria but has said it would use military action to prevent weapons transfers to its enemies.
Israel is widely believed to have been behind a series of airstrikes mainly targeting Iranian and Hezbollah forces in Syria that have joined the country's war fighting alongside the government.
The Syrian state media has said that Israeli missiles targetted the Damascus International Airport on Saturday, with the Syrian military launching projectiles in retaliation.
In the seven years since the last vote was held, more than 360,000 people have been killed, millions more have been forced to flee, and the economy has been crippled.
The elections are being held at a time when Syrian army troops and allied fighters control some two-thirds of the country following the recent advances in southern areas and Damascus suburbs.