A chemical weapons team is set to enter the area after the UN security visit
The head of the chemical weapons watchdog OPCW says a United Nations security team has been shot at in the Syrian city of Douma.
The gunfire on Tuesday was at the site of a suspected gas attack earlier this month.
It has delayed a planned visit by chemical weapons inspectors after the UN security team went in to assess the situation.
Inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) will go in on Wednesday if the UN team decides "the situation is sound", according to Syria's UN ambassador, Bashar Ja'afari.
They will investigate an alleged poison gas attack by the Syrian regime which is said to have killed at least 70 people.
Mr Ja'afari said on Tuesday: "Today the UN security team entered Douma... in order to assess the security situation on the ground and if this United Nations security team decided that the situation is sound in Douma then the fact-finding mission will begin its work in Douma tomorrow.
"The Syrian government did all that it can do to facilitate the work of this mission."
Media in Syria reported that the inspectors had already entered the area, but the US State Department said it understood that the visit was still to take place.
The OPCW travelled to Syria last week to inspect the site of the suspected chemical attack on April 7th.
The head of the OPCW said on Monday its investigators had been prevented from going to the scene by Syria and Russian authorities.
France says it is "highly likely" evidence was disappearing from Douma before weapons experts arrived in the area.
The US, UK and France launched airstrikes against Assad's government on Saturday - targeting a chemical weapons facility - in retaliation for the alleged chemical attack.
British Prime Minister Theresa May insisted it was morally and legally right to target three sites that stored or researched deadly chemical weapons.
Damascus and Moscow have both denied using poison gas and have broadcast statements from hospital workers in Douma - which medical aid groups operating in rebel areas have dismissed as propaganda - saying that no chemical attack took place.
Meanwhile, there is confusion over reported airstrikes in Syria after Syrian state TV said a "false alarm" had set off the country's air defences early on Tuesday morning.
Quoting an unnamed military official, state TV said air defences fired a number of missiles due to a "false alarm", but gave no more information.
Earlier, the same outlet claimed missiles had targeted two airbases - at Shayrat in Homs province and Dumair military airport, northeast of Damascus in overnight raids.
State TV said the country's air defences had confronted a new "aggression" but gave no further details, prompting the US to say its military was not involved.