Israeli jets fired missiles at a military facility in Syria on Thursday, killing two army personnel, the Syrian army claimed.
The strikes caused material damage near Masyaf in the northwestern part of Syria near the Lebanese border, according to the Syrian army, which told state media that the missiles were fired from Lebanese airspace at 2:42 a.m. local time.
The Israel Defense Forces (IDF) refused to comment.
The London-based Syrian Observatory for Human Rights (SOHR) describes the site as a scientific research facility and a short- and medium-range missile depot.
Former Israeli National Security Advisor Yaakov Amidror said the site was one of the Syrian regime's centers of military research and development, which had produced missiles and, in the past, chemical weapons.
The strike marks a new level of alleged Israeli involvement in Syria since the civil war began six years ago, according to Amidror, who served as National Security Advisor between 2011 and 2013.
"It is the first time the target ... is a formal Syrian facility; not just a warehouse, but a center of research and development and [production]," he said.
In its report, Syria's state-run SANA news agency quotes Syria's military accusing Israel of propping up ISIS's "morale," and linking the reported strike with recent military wins over the terror group in the strategic Syrian town of Deir Ezzor.
"This aggression comes in a desperate attempt to raise the collapsed morale of the ISIS terrorists after the sweeping victories achieved by the Syrian Arab Army against terrorism at more than one front, and it affirms the direct support provided by the Israeli entity to the ISIS and other terrorist organizations," the Syrian army said in a statement to SANA.
'Dozens' of strikes
Israel has consistently said it is not taking sides in Syria's civil war.
Even so, Israel has conducted "dozens" of strikes inside Syrian borders since 2011, Israeli Prime Minister Benjamin Netanyahu admitted last year. Additionally, Israel has treated thousands of Syrians wounded in the country's civil war, including rebel fighters.
Israel has repeatedly said there are red lines in Syria which prompt it to act. These include preventing Hezbollah, a key ally of the Syrian regime and an Iranian proxy, from getting its hands on advanced weaponry, and preventing Iran from establishing a permanent presence in Syria.
"[This strike] is within the framework of the [red lines] policy, but it is another level of interfering," Amidror said.
Addressing the threat posed by Iran in Syria, Israel's Defense Minister Avigdor Liberman has said that Israel "reserves complete freedom of action [to protect] the security of Israeli citizens."