Military action against the Syrian regime would be a "tragic mistake", Russia said Sunday, warning the West not to preempt the results of a U.N. probe into alleged deadly chemical attacks.

Moscow warned there was a danger of history repeating itself a decade after the U.S.-led invasion of Iraq, which it opposed, and urged the United States to refrain from any reckless decision.

"We strongly urge those who, by attempting to impose their own results on the U.N. experts, are raising the possibility of a military operation in Syria to use their common sense and refrain from committing a tragic mistake," foreign ministry spokesman Alexander Lukashevich said in a statement.

"All this is reminiscent of events from a decade ago, when the United States bypassed the U.N. and used fallacious information on the presence in Iraq of weapons of mass destruction to launch an adventure, the consequences of which are known to all," he said.

The United States and Britain led the military invasion of Iraq that toppled long-time dictator Saddam Hussein in 2003.

A U.N. mission had failed to find any of the weapons of mass destruction Saddam was suspected of possessing but the Iraqi strongman was known to have repeatedly used chemical weapons.

The United Nations said Sunday its inspectors in Syria could begin work as early as Monday, after Damascus agreed to the probe Sunday during a visit by top U.N. official Angela Kane.

Doctors Without Borders has said 355 people died last week of "neurotoxic" symptoms, after the opposition claimed regime forces unleashed chemicals east and southwest of Damascus last Wednesday causing more than 1,300 deaths.

The regime has denied the charges and in turn accused the rebels of using chemical arms.

Russia took credit for the deal allowing the U.N. inspectors to begin their work, saying it was the result of "relentless efforts" by Moscow with the Syrian regime.

"We are satisfied with the Syrian leadership's constructive approach towards ensuring an effective cooperation with the U.N. mission," the spokesman said.

Washington, which has said that evidence President Bashar Assad's regime used chemical weapons would cross a red line and warrant tougher action, said the Syrian offer was "too late to be credible."

Officials said U.S. President Barack Obama, who held crisis talks Saturday with top aides, would make an "informed decision" about how to respond to an "indiscriminate" chemical weapons attack.

One official told Agence France Presse that based on the reported number of victims and their symptoms, and U.S. and foreign intelligence, "there is very little doubt at this point that a chemical weapon was used by the Syrian regime against civilians in this incident."

Russia -- which together with Iran and China has supported Assad throughout the 29-month-old Syrian crisis -- urged the rebel camp to guarantee the safety of the U.N. team lead by professor Aake Sellstroem.

"It is important that the armed opposition controlling part of Eastern Ghouta ensure that the U.N. mission is able to operate safely and refrain from the kind of armed provocation witnessed against U.N. observers last summer," Lukashevich said.

Opposition leaders already said Friday that U.N. inspectors would have "unfettered" access to areas under rebel control such as Eastern Ghouta on the outskirts of Damascus to investigate the use of chemical weapons.