Syria media outlets reported Tuesday evening explosions were heard around Damascus, in the Al-Kiswah region south of the Syrian capital. It was further reported the strike's target were missiles trained at Israel.
A senior Syrian army official was quoted by the Reuters news agency as saying that, "Israel targeted a Syrian army position south of Damascus."
"The number increased to at least 15, including at least eight Iranians, killed by the missile strikes," the British-based Observatory reported.
The possible attack came after the IDF instructed to open public bomb shelters in the Golan Heights amid Israeli reports of "irregular Iranian movements" in Syria and the ongoing fear of an Iranian strike at Israel in retaliation for the US withdrawal from the nuclear deal and the airstrike on the T-4 Airbase near Homs last month.
The base attacked in Damascus, Arab media reported, housed Iranian forces and was attacked by Israel in the past. Increased Israeli Air Force traffic was also mentioned in the skies over Israel's northern frontier in unconfirmed reports.
There was no immediate comment from Israel, which almost never confirms or denies airstrikes in Syria.
Yedioth Ahronoth military correspondent Ron Ben-Yishai added that it could be gleaned from the Syrian report of an Israeli attack on a base used by Iranian militias that Iranians have been trying to launch missiles or rockets at Israel in the past few days.
Israel has foiled these attempts, Ben-Yishai opined, both by using the media and—reportedly—by launching a preventative attack. It could also be surmised that the targets of Tuesday's attack were missile silos and rocket launchers the Iranians took out of hiding and intended to use—prompting Israel to attack once it discovered it.
A short time after the initial reports, sounds of explosion could be heard south of the capital, with the official Syrian news agency reporting that "Syrian air defenses have intercepted two Israeli missiles."
A Syrian general told Syrian state television, meanwhile, that the Israeli attack was coordinated with the American withdrawal from the nuclear deal, claiming that its purpose was to test Syria rather than destroy the base.
American army officials, for their part, told CNN of a growing fear that Iran was on the cusp of attacking Israel. When the attack takes place was unclear according to intelligence, the officials said, as was its target.
"If an attack takes place, it may not be immediately clear the perpetrator was Iran," one US official said.
Regardless, the United States is closely monitoring to see whether Iran or its proxies carry out offensive actions in Syria, Lebanon—or even in Iran itself.
The US-led coalition against the Islamic State in Syria said Tuesday no changes could be seen in the movement of Iranian troops in the past few days.
Earlier Tuesday, the IDF instructed the opening of shelters in Israel's northern region. Its statement said, "In light of a series of irregular identifications among Iranian forces in Syria, it was decided to make clearer defensive instructions in the Golan Heights region."
At the same time, the US Embassy in Israel published a warning to US government officials, barring the visitation of any Americans to Israel's north without prior approval.
"Consider well whether to visit the Golan Heights until tensions in the region decrease," the statement said. "Increase alertness and look after those around you."
It was reported Monday in Arab media outlets that eight soldiers from the Syrian army's aerial defense force were killed in a mysterious explosion that took place Sunday on the Damascus-Suwayda road.
Engineers and soldiers from said battalion, tasked with operating the S-200 aerial defense system and responsible for downing an Israeli F-16 two months ago, were riding in a transport vehicle when the explosion occurred.
Syrian sources said eight men were killed, and were quick to finger Israel in blame. It was also reported some of the vehicle's passengers actually took part in the downing of the Israeli plane over the Golan.
The Israeli air force attacked a number of Syrian targets in retaliation for the downing.
The T-4 Airbase near Homs was bombed last month, in a strike that was widely attributed to Israel. The Syrian Observatory for Human Rights reported 14 people killed in the missile strike, including senior Iranian officials.
The Hezbollah-affiliated Lebanese Al Mayadeen network, for its part, reported that the missiles that hit the Homs airfield passed through Lebanese airspace, meaning they had come in from the Mediterranean.
Reuters contributed to this story.