Gunmen have abducted six of the International Committee of the Red Cross (ICRC) workers and one Red Crescent volunteer in north-west Syria.
The aid agency has had no contact with the gunmen, an ICRC spokesman says.
Earlier, Syrian state media said gunmen had opened fire on Red Cross staff travelling on the road between Sirmin and Saraqeb in Idlib province.
The ICRC says it has been struggling to gain access across Syria to provide aid to injured and displaced people.
“I am able to confirm that six ICRC staff members and one Syrian Arab Red Crescent volunteer have been abducted near Idlib in north-western Syria,” ICRC spokesman Ewan Watson told Reuters.
“We are calling for their immediate and unconditional release of this team which was delivering humanitarian assistance to those most in need – and we do that on both sides of the frontlines,” he said.
Ewan Watson declined to reveal the identity, gender or nationality of the abducted workers but they are believed to include both local and international staff, who are mainly medical specialists.
Syrian state news agency Sana earlier quoted an unnamed official as saying the workers were abducted and taken to an unknown location after gunmen blocked their path and shot at their convoy.
Ewan Watson was unable to confirm whether or not shots had been fired, but he said the team’s vehicles were also missing.
An ICRC statement said the vehicles they were travelling in had been clearly marked with the Red Cross emblem, “which is not a religious symbol”.
Another ICRC spokesman, Simon Schorno, told Associated Press the attack took place at around 11:30 on Sunday as the team was returning to Damascus.
Simon Schorno said the team had been in the field since October 10 to assess the medical situation and deliver aid in what he described as “a difficult area to go in”.
It is not yet clear who carried out the kidnapping, but Syrian state TV blamed it on what it called “armed terrorists” – a term it frequently uses to describe anti-government rebels.
On Saturday, the Syrian government began the evacuation of around 1,500 civilians, mainly women and children, from a rebel-held Damascus suburb besieged by the army for months.
Many of those coming out of Muadhamiya, south-west of Damascus, were said to be exhausted and traumatized.