United Nations inspectors on Wednesday headed to an area near the Syrian capital Damascus, where there were alleged chemical attacks last week, a UN source said, dpa reported.
"The team is to enter the area of Zamalka, a Damascus suburb, if the security situation there allows for safe access," according to the source, who requested anonymity.
On Monday, the inspectors came under fire from unidentified snipers near Maadamiyet al-Sham, on the outskirts of Damascus.
The team later managed to get to the sites where the opposition claims the regime of President Bashar al-Assad launched toxic gas attacks on August 21, killing at least 1,300 people.
The United States and its allies blame al-Assad's regime for the attacks and have threatened military strikes.
US Vice President Joe Biden said on Tuesday there was no doubt the Syrian regime had used chemical weapons against civilians.
"The president believes, and I believe, that those who use chemical weapons against defenceless men, women and children should and must be held accountable," Biden said.
He added that US national security is strengthened "when we hold accountable those who violate international norms that are the foundation of global security, and ultimately, American security."
Syrian Foreign Minister Walid al-Moallem has warned that his country will defend itself in a way that he said would "surprise" its enemies.