SAINT PETERSBURG (AFP) ― World leaders at the G20 summit on Friday failed to bridge their bitter divisions over U.S. plans for military action against the Syrian regime, as Washington slammed Moscow for holding the U.N. Security Council “hostage” over the crisis.

Despite not being on the original agenda of the summit hosted by Russian President Vladimir Putin outside Saint Petersburg, the leaders discussed the Syria crisis into the early hours of the morning over dinner amid the splendor of a former imperial palace.

Putin has emerged as one of the most implacable critics of military intervention against the regime of Syrian President Bashar al-Assad over an alleged chemical weapons attack on Aug. 21, saying any such move without U.N. blessing would be an aggression.

There was no breakthrough at the dinner as leaders, including U.S. President Barack Obama, presented their positions on the Syria crisis which only confirmed the extent of global divisions on the issue, participants said.

“The differences of opinions of the leaders were confirmed during the dinner,” Kremlin spokesman Dmitry Peskov was quoted as saying by Russian news agencies.

“Some states were defending the view that rushed measures should be taken, overlooking legitimate international institutions. Other states appealed not to devalue international law and not to forget that only the U.N. Security Council has the right to decide on using force,” he added.

A high-ranking source close to the talks said there was a disappointing lack of ambition at the dinner on the Syria issue, noting that Putin as host was keen not to aggravate tensions further.

But a French diplomatic source said the objective of the dinner “was an exchange between the top world leaders and not to come to an agreement.”

The dinner went on into the small hours of the morning and even after a late-night opera show, Putin and British Prime Minister David Cameron had a meeting to discuss the Syria situation, the Kremlin said.

U.N. chief Ban Ki-moon Friday also warned that military strikes could spark further sectarian violence in the country which he said is suffering from a humanitarian crisis “unprecedented” in recent history.

“I must warn that ill-considered military action could cause serious and tragic consequences, and with an increased threat of further sectarian violence,” Ban said.

The Syria crisis and prospect of military intervention has overshadowed the official agenda of the summit of leaders of the world’s top economies and emerging markets to stimulate growth and battle tax avoidance.

It was not immediately clear if the leaders would have another chance to discuss Syria on the summit’s second day or if the main session would focus on purely economic issues.

Several Western states share Putin’s opposition to military action and after the British parliament voted against strikes, France is the only power to have vowed it will join American intervention.

Obama is seeking backing from Congress for military action, putting back the timetable for strikes which had been anticipated even before the two day-summit got underway on Thursday.

The U.S. president held a bilateral meeting Friday morning with President Xi Jinping of China, who like Russia vehemently opposes military action against Syria.

Even as the leaders were setting out their arguments at the dinner, the U.S. ambassador to the United Nations in New York launched a lacerating attack on Russia for holding the Security Council “hostage” over its backing of Assad.

“Even in the wake of the flagrant shattering of the international norm against chemical weapons use, Russia continues to hold the council hostage and shirk its international responsibilities,” Samantha Power told reporters.

Amid a new low in U.S.-Russia tensions, no bilateral meeting as been scheduled between Putin and Obama although officials have left the door open for some informal contact.

According to U.S. intelligence, more than 1,400 people living in rebel-held suburbs of Damascus were killed in the Aug. 21 chemical weapons attack, which involved the use of sarin nerve gas.

The U.S. says the Assad regime was responsible, a claim not accepted by Russia.

Cameron told BBC TV from the G20 summit that Britain had further evidence of the use of chemical weapons in the attack in samples its experts had tested.

With the clock ticking down to strikes, Russia said Syria’s Foreign Minister Walid Muallem would travel to Moscow for talks on Monday.

The two-and-a-half year conflict between Assad and rebels, which began as a popular uprising, has left more than 100,000 people dead.

About a third of Syria’s pre-war 20.8 million population has fled abroad or have been forced from their homes, according to the U.N. refugee agency.