Beirut - Regional players are intervening more and more openly in Syria, some emboldened by the chaos created by the conflict, others desperate to prevent the fall of the regime, experts say.
The conflict between President Bashar Assad's government and rebel forces has divided the Middle East, with his allies - Iran and Lebanon's Hezbollah - lined up against Gulf states which back the uprising.
Israel has publicly refrained from backing one side or the other, but warned that the turmoil must not result in the transfer of advanced weapons to arch-foe Hezbollah.
Over the past week, the Jewish state has reportedly twice carried out air strikes against Syrian military sites, with senior Israeli sources saying they targeted Iranian weapons bound for the Shiite group.
The strikes followed an admission by Hezbollah leader Hassan Nasrallah that the group's members are fighting in Syria.
The leader also pledged that Assad's "true friends" would not allow his regime to fall.
War an attractive target
"Many people are now starting to see this as a zero-sum game," said Salman Shaikh, director of the Brookings Doha Centre.
"If you look around the region, whether it's the Jordanians, the Israelis, Hezbollah and the Iranians... this is becoming much more of an existential struggle."
Since the start of the conflict, the sectarian fault lines dividing the Sunni-led opposition from the regime, which hails from the Alawite minority, a Shi'ite offshoot, have made the civil war an attractive target for regional intervention.
Sunni Arab states in the Gulf have openly backed rebel forces, while Shi'ite Iran and its partner Hezbollah have rallied to Assad's side.
Israel has watched with concern, reluctant to lose a reliable enemy in Assad while increasingly worried both by the Salafist role in the revolt and by the involvement of Iran and Hezbollah, its biggest regional foes.
"We're in a regional proxy war in Syria, it's quite clear, particularly between the key Gulf states and the Iranians and its partners such as Hezbollah," Shaikh said.
Israel's intervention in the conflict may be more opportunistic, analysts there said.
"Israel is actually changing the equation and saying 'From now on, I won't allow what's being going on for 20 years - the transfer of weapons to Hezbollah," Syria expert Eyal Zisser told Israeli army radio.
"I am exploiting the weakness of Bashar who really has his hands tied and who really can't do anything to Israel, and every time that I hear that Iran is transferring weapons to Hezbollah, I won't allow it."
For Hezbollah, which relies on Damascus as a weapons supply route and key regional backer, the fall of the Assad regime would be disastrous.
Iran, which has invested heavily in the Syrian government, is equally intent on maintaining its key foothold in the Arab world.
With the stakes so high and their roles increasingly exposed, regional players have little choice but to admit their interventions and have little to lose by doing so, experts said.
Regionalisation of conflict
"Hezbollah has already declared that it is operational and active in Qusayr" in central Syria, Hezbollah expert Amal Saad-Ghorayeb said.
"The Iranians have admitted in the past that they have advisors there and yesterday we heard them say they were ready to train the Syrians... the involvement of these actors has become more open," she said.
"But I also think that it has increased."
The intervention raises the prospect of a dangerous "regionalisation" of the conflict, the analysts warned.
"With all his problems, Assad does not want to start a war, but he could fire missiles at Israel," the Jewish state's former National Security Council head told Israeli radio.
"Maybe we're treading a very fine line."
Israel's air strikes also raise the spectre of new violence between it and Hezbollah, which fought a devastating war in Lebanon in 2006, or a Syrian response that could swiftly escalate.
Global proxy war
After an emergency cabinet meeting on Sunday, the Syrian government warned that the air raids had made the situation in the region "more dangerous".
"I don't think Hezbollah's going to respond to this," Saad-Ghorayeb said.
"What's problematic is how Syria's going to respond," she said, adding that Damascus was unlikely to respond "conventionally" but would feel forced to produce some reaction to avoid emboldening Israel.
"I think what's required now is for them [Syria] to find a way to respond in an unconventional way that wouldn't drag the region into a war."
For Shaikh, the crisis has already drawn in much of the region, and the opposing stands of the United States, which backs the uprising, and Russia, the regime's strongest ally, pose an even greater threat.
"The danger is that we may get into a global proxy war because we also have great powers... on opposing sides," he said. "Containment should not be seen as an option here, it's not a containable crisis."