Any retaliation by Syria and its allies to limited Western military strikes would be restrained, but large-scale intervention aimed at ousting President Bashar al-Assad would inflame the region, analysts say.

Tensions have ratcheted up dramatically in recent days as Washington has warned Syria's regime it will face action over alleged chemical weapons strikes in Damascus in which hundreds are said to have been killed.

Those tensions became more palpable on Tuesday, when US Defence Secretary Chuck Hagel said his country's forces were "ready to go" if called upon by President Barack Obama.

But, analysts note, the breadth and intensity of the pro-Assad response will depend greatly on the type of action taken against his regime.

"Everything depends on the nature, the extent and the goals of a Western strike and, for the moment, I expect nothing more than a warning strike," said Joseph Bahout, a Syria expert and professor at Sciences Po in Paris.

"In this scenario, neither Hezbollah nor Iran will go too far. We can expect 'lateral and indirect' moves like aggression towards UNIFIL (the UN peacekeeping force in Lebanon) or anonymous rockets against Israel but, in the end, it will not be anything new."

Iran and Russia are Assad's principal international allies, while Lebanese Shiite moviement Hezbollah has fought alongside Syrian army forces against rebels in the country.

But if Western powers press ahead with moves to overthrow the regime, that could change the response tremendously.

"In this case, we cannot rule out an extreme response, particularly from Iran," Bahout said.

"And there is at least one unknown -- Russia's reaction."

Moscow on Tuesday warned a military intervention in Syria could have "catastrophic consequences" for the region, but Russian Foreign Minister Sergei Lavrov has said his country would not get involved in a military conflict.

Syrian Foreign Minister Walid Moallem said the country had defences that would "surprise" the world.

"Syria is not an easy case. We have defences which will surprise others," he told reporters in Damascus.

Moves towards Western retaliation against Damascus seemed to be getting louder as the United States and its allies mull military action.

A top Iranian military chief warned on Sunday that the United States will face "harsh consequences" if it intervenes in Syria over the chemical attack claims.

"For the moment, Iran is launching warnings, but if the Americans decide to intervene, they will fall into their (Iran's) trap," said Amir Mohebian, an analyst and journalist based in Iran.

"Iran will sit back and watch as the Americans and their allies sink into a quagmire."

But Bassam Abu Abdullah, head of the Damascus Centre for Strategic Studies, says even a limited conflict could degenerate into something broader.

"The Americans could strike to preserve their image with their allies who have criticised their inaction, to take a position of strength as compared to Russia in peace negotiations and to give a boost to rebels on the ground," he said.

But, "if such a strike does happen, it will not stop there, because the other side will respond... and the whole region will be embroiled in a regional war."

"For now, though, none of the actors want to show their hand."

Ibrahim al-Amine, head of Al-Akhbar, a Lebanese daily that is seen as close to Syria as well as Hezbollah, echoed those remarks.

"Who can guarantee that things will stop at that point," he asked.

"Who can guarantee that such a confrontation will not degenerate into a wider war and that a strike will not open the gates to hell?"

Assad has warned Washington against such a strike, but has not revealed the outlines of a response.

"The United States faces failure just like in all the previous wars they waged, starting with Vietnam and up to our days," he said.

On Tuesday, Muallem defiantly vowed that the country would respond forcefully to any attack.

"We have two options: either to surrender, or to defend ourselves with the means at our disposal," he told a press conference in Damascus.

"The second choice is the best: we will defend ourselves."

For Damascus's allies, the red line looks to be military action targeting the overthrow of the regime.

In late April, Hezbollah chief Hassan Nasrallah said Damascus "has true friends in the region who will not allow Syria to fall into the hands of the United States, Israel and 'takfiri' groups," referring to Sunni extremists.

"If the situation gets more dangerous, states, resistance movements and other forces will be obliged to intervene effectively in the confrontation on the ground," he added.

Indeed, at least one organisation has already threatened retaliation in the event of such strikes.

"The regional interests of those who participate in aggression against Syria would be legitimate targets," said Anwar Raja, a Damascus-based spokesman for the Popular Front for the Liberation of Palestine-General Command.

Syria's diminished security forces
Paris (AFP) Aug 27, 2013 - Following is a breakdown of estimated security forces loyal to Syrian President Bashar al-Assad, according to the The Military Balance 2013, published in March by the International Institute for Strategic Studies in London.

On paper the Syrian army remains one of the biggest in the Middle East, but its fighting capacity has been cut roughly in half by the country's civil war, the IISS estimates.

- Troops: The Syrian army consists in theory of 178,000 troops, including 110,000 in the army, 5,000 in the navy, 27,000 in the air force and 36,000 in air defences.

In 2009, the total number was estimated at 325,000, of which 220,000 were army troops.

"The nominal pre-war strength of the army has likely been reduced by half: the result of a combination of defections, desertions and casualties," IISS experts said.

"Most formations are now understrength. Some brigades are reported to have been disbanded because of either political unreliability or heavy casualties."

Owing to disorganisation stemming from the civil war, the IISS said it was unable at present to accurately estimate the strength of Syrian paramilitary forces, which have played a key role in the fighting.

In 2009, they were estimated at 108,000, including 8,000 in the gendarmerie, under the authority of the interior ministry, and 100,000 in the popular militia of the Baath party, which has been in power since 1963.

As regards reservists Syria's army has 314,000 troops, while there are 4,000 in the navy, 10,000 in the air force and 20,000 in the air defences.

- Structure: The ground army has seven armoured divisions in principle, three mechanised infantry divisions, two special forces divisions and a Republican Guard, created in 1976 and charged with state security.

The fighting capacity of the special forces and the Republican Guard is considered to be superior to that of the regular army.

The IISS estimates that with special forces dominated by Assad's Alawite minority, the Republican Guard and the 3rd and 4th army divisions, the regime is backed by 50,000 elite troops.

- Equipment: the army is equipped with mainly Russian-made materiel, and included 4,950 tanks when fighting began.

It has nonetheless suffered "significant losses of armour, while the air force has also lost some combat aircraft and helicopters."

Syria has a large arsenal of missiles, the command of which is based in the northern city of Aleppo.

The navy has two frigates. The air force has in principle 365, mainly Soviet-built, fighter planes. They numbered 555 in 2009.

"The level of readiness of a significant element of the air force's combat aircraft inventory is likely poor," the IISS noted.

Air defence units appear to have been the least affected by the fighting, and are equipped with several thousand Russian ground-air missiles, including some recent and potentially effective models.