Israeli warplanes launched strikes on multiple military targets, including air defense units and surface-to-surface missile depots, according to the Syrian Observatory for Human Rights.
The monitor described the attacks as the "heaviest strikes" on Syria's coastal region since Israel began its air campaign in 2012.
Explosions from the strikes were so powerful that they registered as a magnitude 3.0 event on seismic sensors, researcher Richard Cordaro said. He noted the blast signal traveled nearly twice as fast as that of a standard earthquake, reaching a magnetometer station 820 kilometers away in Isnik, western Turkey.
Dramatic videos circulating online showed a massive fireball illuminating the night sky, followed by several secondary explosions that sent a large mushroom cloud into the air.
The targeted area, Tartus, is home to one of Russia's two military bases in Syria, established in 1971 by the Soviet Union and used primarily as a naval and logistical hub. The facility was expanded in 2017 after Syrian President Bashar al-Assad granted Russia a 49-year lease in exchange for Moscow's military support during the war on terror.
Satellite imagery reviewed earlier this week suggested that Russia has pulled back from the Tartus base following the fall of Damascus on December 8. Five warships observed in the port last week had departed by Monday.
The recent airstrikes raise questions about the future of Russia's military presence in Syria, including its Hmeimim airbase near Latakia, which was critical to Russian operations in the region.
Moscow confirmed earlier this week it had begun evacuating some diplomatic staff from Syria. A Kremlin spokesperson said on Wednesday that Russia remains in contact with Syria's new authorities regarding its military bases.
The strikes came amid shifting dynamics in the region after a coalition of rebel forces, led by the militia group Hayat Tahrir al-Sham (HTS), overthrew Assad following an 11-day offensive. Assad fled to Russia with his family after reportedly being persuaded by Russian intelligence to abandon the capital.
United Nations envoy for Syria Geir Pedersen condemned the strikes last week, calling them a "very troubling development" that must cease immediately.