A first case of coronavirus was identified in north-west Syria on Thursday, reviving fears of the pandemic reaching the rebel bastion's refugee camps.
Mahmoud Daher, head of the World Health Organisation's office in Gaziantep, Turkey, said the patient was a male Syrian doctor in his 30s, working in a hospital in Bab Al Hawa, on the Syrian-Turkish border.
"He suspected that he might have contracted Covid-19," Mr Daher said.
The test came back positive on Thursday, he said, confirming it was the first in north-west Syria.
"The hospital has been closed as have its living quarters," opposition Health Minister Dr Maram Al Sheikh said.
Those who had been in contact with the patient had been swabbed and isolated, and an emergency meeting was convened, Dr Al Sheikh said on Twitter.
Aid groups have been preparing for months to prevent an outbreak in north-west Syria, where a fragile truce has stemmed a regime offensive against the Idlib region.
The extremist-dominated region is home to about three million people, many living in crowded camps after being forced to flee their homes during nine years of war in Syria.
Mr Daher said the discovery of a first case was "worrying because of the conditions".
"We need to enhance our work with all authorities and service providers to make sure that no further transmission of Covid-19 can happen," he said.
"Otherwise, it might become a real problem."
Syria has officially recorded 372 cases of coronavirus, including 14 deaths in government-held areas.
In the Kurdish-controlled north-east, the UN has recorded six cases including one death.
There are fears the outbreak in the country is much larger than officially reported because of the widespread lack of testing.