About 30 Lebanese Hezbollah fighters and 20 Syrian soldiers and militiamen loyal to President Bashar al-Assad have been killed in the fiercest fighting this year in the rebel stronghold of Qusair, Syrian activists said on Monday.
If confirmed, the Hezbollah toll from Sunday's battles in Qusair near the Lebanese border would highlight a deepening intervention in Syria by the guerrilla group set up by Iran in the 1980s to fight Israeli occupation troops in south Lebanon.
The reported Hezbollah losses also reflect the extent to which the Syrian conflict is turning into a proxy war between Shi'ite Iran and U.S.-aligned Gulf Arab states such as Saudi Arabia and Qatar, which back Assad's mostly Sunni foes.
Western countries and Russia, an ally of Damascus, back opposing sides in this regional free-for-all which is also sucking in Israel. Three times this year Israeli planes have bombed presumed Iranian arms stocks destined for Hezbollah.
Israeli Prime Minister Benjamin Netanyahu said his country was "preparing for every scenario" in Syria and held out the prospect of more Israeli strikes inside Syria to stop Hezbollah and other opponents of Israel getting advanced weapons.
Israel has not confirmed or denied reports by Western and Israeli intelligence sources that its raids targeted Iranian missiles stored near Damascus that it believed were awaiting delivery to Hezbollah, which fought a war with Israel in 2006.