Syria's foreign ministry said Thursday that a salvo of Israeli strikes on its territory marked a "new phase" of direct involvement in the country's seven-year conflict.
In a statement carried by state news agency SANA, it said Israel's "direct confrontation... signals the start of a new phase of the war on Syria".
Israel's army said it hit dozens of Iranian military targets in Syria overnight.
Israel's "aggressive behavior... will not lead to anything but an increase in tension in the region", the ministry said.
It was "a serious threat to international peace and security", the ministry said.
The Syrian Observatory for Human Rights, a Britain-based monitor, said the strikes near Damascus, as well as in the center and southwest of the country, killed 23 regime fighters.
The Syrian army said just three people had been killed.
The raids overnight were the latest in a series of alleged Israeli strikes inside Syria.
On April 29, missile strikes -- "probably Israeli" -- on regime military positions killed at least 26 mostly Iranian fighters, according to the Observatory.
On April 9, missiles targeted the T-4 air base in the central province of Homs, killing up to 14 fighters, including seven Iranians, two days after an alleged chemical attack carried out by the Syrian regime.
Damascus accused Israel of carrying out the strike.
Since the start of Syria's civil war in 2011, Israel has repeatedly targeted positions of the Syrian army and Lebanon's Shiite movement Hezbollah backing it inside the country.