Syria's suffering opens a door for Washington

Turkish artillery is firing across the border into Syria. Explosions have torn apart buildings in Aleppo, Syria's largest city, making their floors collapse on top of each other so they look like giant concrete sandwiches. The country resembles Lebanon during its civil war, the victim of unbearable and ever-escalating violence but with no clear victor likely to emerge.

In Iran, Syria's most important ally in the region, sanctions on oil exports and central bank transactions are paralysing the economy. The bazaar in Tehran closed after violent protests at a 40 per cent fall in the value of the currency, the rial, over the past week. Demonstrators gathered outside the central bank after finding they could no longer get dollars from their accounts. Popular anger is at its highest level since the alleged fixing of Iran's presidential election of 2009.

Will these events lead to a change in the balance of power at the heart of the region? Iran and Syria were the leaders for the past 10 years of the so-called "resistance bloc", the grouping that supported the Palestinians and opposed the US-led combination that brought together Arab dictatorships and Israel in a tacit alliance. This anti-American bulwark was at the height of its influence between 2006 and 2010 after the failed US invasion of Iraq and Israel's bombardment of Lebanon and Gaza.

At first, the Arab Spring seemed to favour the "resistance bloc". Without Syria and Iran having to lift a finger, President Hosni Mubarak and President Zine el-Abidine Ben Ali were driven from power in Egypt and Tunisia. And Bashar al-Assad seemed confident, in the first months of 2011, that his opposition to the US, Arab autocracies and Israel would protect him against the revolutionary wave.

Eighteen months later, it is the "resistance bloc" that is fighting for its life. Turkey is becoming ever more menacing to Syria and impatient of American restraint. After the US presidential election, Washington could well decide that it is in its interests to go along with Turkish urgings and give more military support to the Syrian opposition. The US might calculate that a prolonged and indecisive civil war in Syria, during which central government authority collapses, gives too many chances to al-Qa'ida or even Iran. It has had a recent example of how a political vacuum can produce nasty surprises when the US ambassador to Libya, Christopher Stevens, was killed in Benghazi last month.

An ideal outcome from the American point of view is to seek to organise a military coup against the Syrian government in Damascus. Zilmay Khalilzad, a former US ambassador to Iraq and Afghanistan, wrote recently in Foreign Policy magazine that the US should take steps "empowering the moderates in the opposition, shifting the balance of power through arms and other lethal assistance, encouraging a coup leading to a power-sharing arrangement, and accommodating Russia in exchange for its co-operation".

By becoming the opposition's main weapons' suppliers, the US could gain influence over the rebel leadership, encourage moderation and a willingness to share power. Mr Khalilzad envisages that these moves will prepare the ground for a peace conference similar to that held at Taif in Saudi Arabia in 1989 that ended Lebanon's 15-year civil war. It is also what the US would have liked to have happened in Iraq after 1991.

More direct military involvement in Syria could be dangerous for the US in that it could be sucked into the conflict, but outsourcing support for the rebels to Saudi Arabia and the Sunni monarchies of the Gulf may be even riskier. Arms and money dispensed by them are most likely to flow to extreme Sunni groups in Syria, as happened when Pakistani military intelligence was the conduit for US military aid to the Afghan Mujahideen in the 1980s.

Instead of a fight to the finish – and that finish would probably be a long way off – a peace conference with all the players may be the only way to bring an end to the Syrian war. But it is also probably a long way off, because hatred and fear is too deep and neither side is convinced it cannot win. The Kofi Annan plan got nowhere earlier this year because the government and rebels would only implement those parts of it that favoured their own side.

How does Iran view its endangered regional position in the Middle East? Iran's policy is usually a mixture of practical caution and verbal crudity – the latter often represented to the outside world by President Mahmoud Ahmadinejad. But in its struggles with the Americans in Iraq after 2003, Iran was realistic and seldom overplayed its hand. It may be under pressure from sanctions now, but its situation is nothing like as serious as it was during the Iran-Iraq war of 1980 to 1988. More recently, Iranians joked that only divine intervention could explain why the US had disposed of its two main enemies, the Taliban and Saddam, in wars that did more good to Iran than the US.

But the success of sanctions on oil exports and Iranian central bank operations seems to have caught Tehran by surprise. Oil revenues have fallen and the cost of food, rent and transport is up. In recent years, Iranians have become big foreign travellers, but last week were stopped withdrawing rials from their dollar accounts. No wonder they're angry.

But enemies of the Iranian regime should not get up their hopes too early. An Iranian journalist in Tehran sympathetic to the opposition said to me last year that "the problem is that the picture of what is happening in Iran these days comes largely from exiled Iranians and is often a product of wishful thinking". The Iranian regime is far more strongly rooted than the Arab regimes overthrown or battling for survival. The Iranian-led bloc in the region may be weaker, but it has not disintegrated.