The threat of a major war and deep US-Russian tensions over Syria have overshadowed the St. Petersburg G20 summit of leaders of the world’s 20 largest economies. The summit’s ostensible main agenda item—crises in “emerging market” economies such as India and Turkey—has been subsumed into discussion of the devastating global economic impact of a new war in the Middle East.

In the hours before the summit, Iranian officials indicated they were prepared to go to war to defend their ally, Syrian President Bashar al-Assad, against a US-Israeli attack. Iranian Supreme Leader Ayatollah Ali Khamenei said that Washington and its allies “are using [allegations of] chemical weapons use as a pretext … saying that they want to intervene for humanitarian reasons.”

The commander of Iran’s Quds Force, Qassem Soleimani, issued a statement declaring: “The aim of the United States is not to protect human rights, but to destroy the front of resistance [against Israel]. We will support Syria to the end.”

An account of an August 25 meeting in Tehran between United Nations Undersecretary-General Jeffrey Feltman and Iranian officials leaked to Egypt’s Al Ahram newspaper gave more details on Iranian plans. The Iranian officials said they could guarantee that Syria had not used chemical weapons. They indicated that if, however, Israel joined a US attack on Syria, they would go to war to defend Syria.

Israel has already mounted several air strikes on Syrian targets in recent months and has long battled Lebanon’s Hezbollah organization, which has been drawn into the fighting on Assad’s side. There is a real potential for both Israeli and Iranian intervention in a Syrian war launched by Washington, France and their allies, setting the stage for a broad regional war.

In the opening hours of the G20 summit Thursday, Russian spokesmen reported that the BRICS countries (Brazil, Russia, India, China and South Africa) had warned of the economic effects of a war in Syria. There is particular concern over the impact on the price and supply of oil should a US-Iranian conflict shut down the Persian Gulf oil trade.

Chinese Vice-Finance Minister Zhu Guangyao warned that “military action would definitely have a negative impact on the global economy, especially on oil prices.”

BRICS officials also criticized the US Federal Reserve’s plans to start winding down its “quantitative easing” money-printing program. They complained that the Federal Reserve was undermining their economies by feeding expectations of higher interest rates in the United States and thereby encouraging investors to pull capital from so-called “developing” economies and invest it in the US to get higher returns. Russian and Brazilian officials called on Washington to coordinate monetary policy with other governments.

During the summit meeting itself, British Prime Minister David Cameron defended his decision to submit the question of Britain’s participation in the war to a vote in Parliament. In a stunning defeat for Cameron, the Parliament last week voted against military action as it emerged that Cameron had no evidence to support US, British and French charges that Assad carried out a chemical attack in Ghouta.

Cameron denounced those who opposed his case for war with Syria, saying they failed to take a “stand against the gassing of children” and had to “live with the way they voted.”

Russian officials pointed out that Washington had no evidence to support its charges that Assad used chemical weapons. They called on Washington to let the UN conclude its investigation into the attacks.

Several other G20 countries, including Brazil, Mexico and India, called for the UN to oversee investigations and negotiations. South Africa and Brazil stressed that unilateral action against Syria by the United States and its allies—France, Turkey and the Persian Gulf oil sheikhdoms—would be in violation of international law.

The US-led war drive against Syria underscores the collapse of the international legal order and intensifying divisions between the major powers.

With France, due to Cameron’s defeat, currently the only European country preparing to participate in a US assault on Syria, the impending war is provoking a diplomatic crisis within the European Union. EU President Herman Van Rompuy issued a statement yesterday calling for the Syria crisis to be addressed “through the UN process.” He also declared that “there is no military solution to the Syrian conflict.”

Van Rompuy added, “As to what the European Union’s reaction will be if there is a military intervention by France, we do not yet know. We are working on this.”

France’s conservative daily Le Figaro wrote bitterly that this was a “slap in the face” of French President François Hollande and an alignment of the EU with German foreign policy.

Above all, the Syrian war is bringing to the fore the conflict between the US and Syria’s main ally, Russia, which views Washington’s promotion of Islamist terrorist groups in the Middle East as a threat to its interests in Eurasia and its own internal security. (See: NATO’s Afghan draw-down stokes Kremlin’s fears of clash with US ).

With the CIA and its European and Arab allies arming the Islamist opposition in Syria, Russia has deployed a naval flotilla off the Syrian coast even as Washington has sent warships to the eastern Mediterranean to prepare missile strikes on Syria. The Kremlin has also sold Assad portions of a high-tech S-300 anti-aircraft defense system.

At the same time, Russian officials have repeatedly signaled their interest in reaching a settlement with Washington. On Wednesday, Russian President Vladimir Putin said he did not rule out supporting US military action against Syria if the UN produced proof that Assad’s forces had carried out chemical attacks. He also confirmed that he had frozen delivery of further S-300 parts to Syria.

On Thursday, Russian officials made further conciliatory statements, claiming that Russia’s naval deployments in the Mediterranean were primarily intended to evacuate its citizens from Syria. These remarks did nothing to slow Washington’s war drive, however, and the standoff between Russian and US ships in the eastern Mediterranean continues.

Several weeks ago, Obama snubbed Putin, canceling a planned post-G20 summit meeting between the two. The ostensible reason for the diplomatic rebuke was Russia’s decision to grant temporary asylum to National Security Agency (NSA) whistleblower Edward Snowden. Tensions over Snowden have now been compounded by Washington’s preparations to launch an unprovoked war of aggression against Russia’s ally, Syria.

In congressional testimony Wednesday, US Secretary of State John Kerry said it was “basically incorrect” to view the Syrian opposition as dominated by Al Qaeda. In making this assertion, Kerry ignored official US findings that Al Qaeda-linked militias have carried out hundreds of terror bombings in Syria.

Putin commented, “We talk to [US officials] and we assume they are decent people, but he is lying and he knows he is lying. This is sad.”

These rising diplomatic and military tensions reflect the inability of any government to halt the drive to war, which can be fought only on the basis of the mobilization of the working class in struggle against capitalism. Six years ago, Putin responded to the Bush administration’s threats to launch a war with Iran by declaring that such a conflict would lead to World War III. Today, the drive to war against Syria poses the danger of precisely such a conflict.