The TV gave no further details.
Syrian state media are saying that dozens of civilians who had been held for years by a rebel group near the capital of Damascus have been set free.
The toll is likely to rise, said the Union of Medical Care Organizations (UOSSM), a group of worldwide aid agencies.
The Syrian president became more aggressive towards rebel groups and in turn, they had agreed to leave Douma within two days. The Pentagon, however, denies any role in the air strikes.
According to the source, the Syrian air defense systems shot down eight missiles while repelling the attack.
Most of those killed were either Iranians or members of Iran-backed groups, said Rami Abdurrahman, who heads the observatory, which has regularly monitored Syria's seven-year war.
Lebanon's National News Agency on Monday said Israeli warplanes were flying near the country's border with Syria. "The Israeli aggression on the T4 airport was carried out with F-15 planes that fired several missiles from above Lebanese land", state news agency SANA said.
AP quoted SANA saying it was "likely to be an American aggression" though US officials told the organization no American military action had been taken.
Syria's state news agency says missiles have struck an air base in central Syria in the early hours of the day.
The Pentagon said: "The Department of Defense is not conducting air strikes in Syria". At least 40 people were killed in that assault, including families found in their homes and shelters, opposition activists and local rescuers said.
The strikes reportedly caused an unknown number of deaths.
"On the eve of potential United States and French strikes against Assad in response to the Douma gas attack, it is likely the Israelis already had the intention to strike at the T-4 base, and timed their attack to maximise the destruction they could inflict on Iranian forces", he told AFP.