Syria has asked the United Nations to try to "prevent any aggression" against it, state news agency SANA said Monday, as the United States weighs military action against Damascus.

"The Syrian government calls on the UN secretary general to assume his responsibilities... and to make efforts to prevent any aggression against Syria," the agency said, quoting a letter from Syria's UN representative Bashar al-Jaafari.

The letter also urged the United Nations to help seek a "peaceful political solution to the crisis" in Syria, where more than 110,000 people have been killed in violence since an uprising against the regime began in March 2011.

US President Barack Obama is seeking approval from Congress for military action against Syria in response to an alleged chemical attack on Damascus suburbs on August 21 that killed hundreds.

Much of the international community, including the United States, Britain and France, has accused the Syrian regime of carrying out the attack, a charge that the government in Damascus denies.

US Secretary of State John Kerry on Sunday said Syria used sarin gas and France on Monday was set to provide what it says is clear evidence the regime was behind the alleged chemical attack.

"The Syrian government repeats once again that it has never used chemical weapons," Jaafari wrote in the letter.

"The world was expecting the United States to play its role as a sponsor of peace... by preparing seriously for the Geneva conference on Syria, and not as a country that uses military force against those who oppose its policies," he added.

Earlier in the year, the United States and Russia said they would work to organise a peace conference in Geneva to seek a political solution to the Syrian conflict.

But the efforts have gradually fallen apart, with leaders announcing successive delays to the mooted meeting.

Russia's Foreign Minister Sergei Lavrov said Monday that military action against Damascus would put off chances for a peace conference "a long time, if not forever."