Western nations have "hard evidence" that chemical weapons have been used at least once in the Syrian war but a UN investigation is now unlikely to get into the country.
UN Secretary General Ban Ki-moon "remains convinced that the use of chemical weapons by any party (in Syria) under any circumstances would constitute an outrageous crime".
Myanmar on Thursday denied accusations it had used chemical weapons against ethnic minority rebels in the northern state of Kachin, where an escalating conflict has overshadowed wider political reforms.
Russia said on Monday it would be "political suicide" for the government of Syrian President Bashar al-Assad if it used chemical weapons against the armed opposition.
US Secretary of State Hillary Clinton on Monday issued a "strong warning" to the regime of Bashar al-Assad over the potential use of chemical weapons against the Syrian people.
South Korea on Friday launched a full inquiry into a toxic chemical leak in the southeastern city of Gumi, as officials considered designating the affected area a "disaster zone".
Iran on Monday added its voice to warnings against Syria ever using chemical weapons in its increasingly large-scale war with anti-government insurgents.
The Syrian regime plans to deploy chemical weapons against its own people "as a last resort", the former head of Syria's chemical arsenal told The Times newspaper in an interview published Wednesday.