Associated Press reporters in Damascus heard heavy airstrikes overnight and into Tuesday on the city and its suburbs. Photographs circulating online showed destroyed missile launchers, helicopters and warplanes.

The Syrian Observatory for Human Rights, which relies on a network of sources around Syria, said Israeli strikes had "destroyed the most important military sites in Syria".

The group said the strikes targeted weapons depots, boats from the Assad government's navy, and a research centre.

Near the port city of Latakia, Israel hit an air defence facility and damaged Syrian naval ships as well as military warehouses. 

In and around the capital Damascus, strikes targeted military installations, research centres and the electronic warfare administration. 

The Britain-based Observatory, which has closely tracked the conflict since the civil war erupted nearly 14 years ago, said Israel has carried out more than 300 airstrikes across the country since rebels overthrew Assad over the weekend.

There was no immediate comment from the armed groups — led by Hayat Tahrir al-Sham (HTS), – that have taken control of Damascus.

Israel had earlier seized a roughly 400-square-kilometer (155-square-mile) buffer zone between the occupied Golan Heights and Syria that had been established after the 1973 Mideast war.

Israel has also said it is striking suspected chemical weapons sites and heavy weapons.

Israel has a long history of seizing territory during wars with the Arab countries and occupying it indefinitely, citing security concerns.

Israel occupied the Golan Heights from Syria in the 1967 Mideast War.

The Observatory and Beirut-based Mayadeen TV said Israeli troops are advancing up the Syrian side of the border with Lebanon. 

An Israeli military official said troops plan to seize a buffer zone inside Syria as well as “a few more points that have strategic meaning," without elaborating.

Egypt and Saudi Arabia have condemned Israel’s incursion, accusing it of exploiting the disarray in Syria and violating international law.

* This story was edited by Ahram Online.