At least nine pro-regime fighters died in a suspected Israeli missile attack during the night in northern Syria, according to a monitor on Monday.
Syrian state media have accused Israel of bombing a military position in Aleppo province on Sunday, which would have been a rare Israeli attack in the war-torn country.
The Syrian Observatory for Human Rights, a war observer stationed in Britain, said the base was used by the Syrian regime, the arch-rival of Iran.
"Israeli missiles have attacked a center of the Iranian Revolutionary Guard near the military air base Neirab," said the head of the Rami Observatory Abdel Rahman.
He said the killers contained at least six Syrians, but they could not declare the nationalities of the other fighters.
The location is a logistics center used to provide equipment and food for pro-government forces fighting on nearby fronts, but has not stored weapons, Abdel Rahman said.
Tehran has deployed armed forces to support the efforts of Syrian President Bashar al-Assad to crush a seven-year uprising against his government.
Assad said that the armed forces were consultants, but denied the presence of Iranian fighters on Syrian territory.
Last Sunday, the state press agency SANA said Israeli missiles were hit near a strategic air base, but said it did not have casualties.
"The Zionist enemy … aimed his missiles at one of our military positions north of the military air base in Neirab, but the damage was material," he said, citing a military source.
The Israeli army refused to comment on the reports.
The attack is the third suspected Israeli attack on Syria this month alone.
Damascus accused his archenemy of taking military position in central Syria on July 8, and Israel said he had reached three military posts in the country a few days later.
The alleged Israeli attacks usually hit army positions near Damascus and in the central provinces of Homs and Hama, but were rarely in the north like Aleppo.
Israel has repeatedly warned that it will tolerate a trenched presence of its arch-enemy Iran in neighboring Syria.
In May, it launched an unprecedented strike wave against dozens of Iranian military targets in Syria.
Israel has been on alert in recent weeks as Assad's forces fight to reconquer parts of southern Syria on the border with the Golan Heights, annexed by Israel.
After taking most of the main province of Daraa, government forces are launching an offensive in the neighboring province of Quneitra, which is largely owned by the rebels.
They started on Sunday morning with heavy bombing in the area and on Monday the air raids continued, the observatory said.
The state SANA news agency said the missile attack near a strategic air base in the province of Aleppo, far north, usually the alleged Israeli attacks occur