Angela Kane, who was dispatched by the UN secretary-general to push for a speedy investigation into Wednesday's purported attack outside the Syrian capital, did not speak to reporters upon her arrival in Damascus.
The US, Britain, France and Russia have all urged the Assad regime and the rebels fighting to overthrow him to cooperate with the United Nations and allow UN experts already in Syria to look into the latest purported use of chemical agents.
Anti-government activists accuse the Syrian government of carrying out a toxic gas attack on the eastern suburbs of Damascus on Wednesday and have reported death tolls ranging from 136 to 1,300. Even the most conservative tally would make it the deadliest alleged chemical attack in Syria's civil war, now in its third year.
The Assad regime has denied the claims that it was behind the chemical attack, calling them "absolutely baseless" and suggesting they are an attempt to discredit the government.
Today, Syrian state media reported that several government troops who took part in an offensive on a rebel-held neighbourhood in the capital were experiencing severe trouble breathing. The official news agency, SANA, said initial reports indicate several cases of "suffocation" among Syrian troops trying to storm the Jobar district in east Damascus today.
SANA said ambulances were rushing the affected soldiers to the hospital for treatment.
The report appeared to be implying that rebels in Jobar were using a chemical agent, which would induce such symptoms, against government troops.
The UN experts already in Syria are tasked with investigating three earlier purported chemical attacks in the country: one in the village of Khan al-Assal outside the northern city of Aleppo in March, as well as two other locations that have been kept secret for security reasons.
It took months of negotiations between the UN and Damascus before an agreement was struck to allow the 20-member team into Syria to investigate. Its mandate is limited to those three sites, however, and it is only charged with determining whether chemical weapons were used, not who used them.