Nine team members have been deployed in the wake of the alleged chemical attack earlier this month
Chemical weapons inspectors are reported to have arrived in the Syrian city of Douma - where dozens of people are said to have died in a gas attack.
It came following apparent delays in the inspectors being allowed enter Douma.
The Syrian state-run news agency SANA today said: "The fact-finding team from the Organization for the Prohibition of Chemical Weapons (OPCW) entered Douma city in Eastern Ghouta area in Damascus countryside on Tuesday."
It had previously been suggested the team would gain access to the site on Wednesday.
The US has previously voiced concerns though that Moscow may have already "tampered" with evidence in the city.
Rescue workers on the ground alleged the chemical attack took place on April 7th.
The US, along with France and the UK, has publicly blamed the regime of Bashar al-Assad for the alleged attack - claims denied by both the regime and its ally Russia.
In a briefing on Monday the CEO of the OPCW, Ahmet Üzümcü, said a team of nine inspectors was set up on April 9th.
He said some of the team members were called back from other missions and training courses, and they they have all volunteered for this mission.
On April 10th the OPCW handed a note to the Syrian delegation, notifying them of their decision to deploy "as early as possible", as well as the names of the team members for visas.
The OPCW said it also received a letter from the ambassador of the Russian Federation, supporting the Syrian request.
Mr Üzümcü added: "The UN Secretary-General called me on Tuesday April 10th and expressed full support for the work of the OPCW in Syria and promised to provide all assistance that we may need. I have also been in touch with the UN High Representative for Disarmament Affairs".
An advance group of three experts from the fact-finding mission arrived in Beirut on Thursday, while the remaining six members joined them on Friday.
On Saturday the team travelled to Damascus, where they met with officials to work out a plan for the deployment.
Before being allowed enter the city, the team was told by Syrian authorities that they could interview 22 witnesses who could be brought to Damascus.
The US, France and UK over the weekend launched missile attacks at sites in Syria in response to the alleged attack, reportedly targeting sites involved in the production of chemical weapons.
Earlier today, Syrian officials claimed airstrikes had targeted two airbases in Homs and Damascus - triggering the country's air defence systems.
However, it was later revealed to have been a 'false alarm', although no additional information about the incident was released.
Reporting by Jack Quann, Stephen McNeice and IRN