The source did not say when the inspectors might visit the site, or whether a planned visit to Douma on Wednesday had been postponed.
But on Wednesday, OPCW said that's not what happened.
A mission by experts with the United Nations chemical watchdog, who were supposed to enter the Syrian town of Douma to examine the circumstances surrounding an alleged chemical attack, has been once again delayed due to unexpected gunfire at the site near Damascus.
OPCW inspectors have to date compiled an excellent and massive record of on-site inspections - 6,785 inspections at weapons-related and industry sites in 86 countries.
But the OPCW says the United Nations security team came under fire and there was an explosion after it entered one of the sites.
NPR's Ruth Sherlock says that nobody was reportedly injured in the attack.
Despite claims by the U.S. military that all missiles hit their targets, the Russian defense ministry said after the attack that 71 missiles were intercepted by Syria's air defense, which relies on Russian equipment.
OPCW chief Ahmet Uzumcu said the incident highlighted "the highly volatile environment" in which the fact-finding team had to work.
"We would like (Indonesia) to join us in holding the Assad regime accountable for the misuse and the abuse of the Chemical Weapons Convention and the use of chemical weapons against Syrian nationals", said UK's Ambassador to Indonesia Moazzam Malik after the meeting.
Today's news comes as the Pentagon warned the Syrian government still had the capability to launch a fresh chemical attack.
"For a new diplomatic initiative to work, the balance on the ground must be changed", said Nabeel Khoury, a former USA diplomat who is now a fellow at the Atlantic Council think-tank.
Syrian President Bashar al-Assad is now in his strongest position since the early months of a seven-year-old civil war that has killed more than 500,000 people and driven more than half of Syrians from their homes.
"The U.S. ambassador to the OPCW, Kenneth Ward, expressed Washington's concern that almost two weeks after the attack, inspectors would find tampering of evidence".
He added the sites the team wants to visit were under the control of the Russian military police.
The fact that the strike took place on the very same day as when Damascus and Moscow-invited OPCW probe mission was to start work shows an intention to disrupt investigations for fear they might confirm Russian specialists' findings that no traces of chemical agents were found at the site, nor alleged victims were admitted at nearby hospitals.
The Russian foreign ministry dismissed that as fake news. 'I can guarantee that Russian Federation has not tampered with the site, ' he told the broadcaster.
OPCW inspectors arrived in Damascus on April 14 and had planned to head to Douma, on the outskirts of the capital, on April 16. We didn't know what to do.