The humanitarian agency had no contact with the unidentified gunmen but was appealing for the seven to be freed immediately, ICRC spokesman Ewan Watson said, declining to reveal the nationalities or gender of the six ICRC staff for now.
"I am able to confirm that six ICRC staff members and one Syrian Arab Red Crescent volunteer have been abducted near Idlib in northwestern Syria," Watson told Reuters in Geneva.
"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.
Syrian state media reported the incident earlier in the day, saying the gunmen had kidnapped the Red Cross workers after opening fire on their vehicles on Sunday.
Quoting an unnamed official, state news agency SANA said the workers were travelling in the Idlib area when gunmen blocked their path, shot at their convoy, seized them and took them to an unknown location.
"An armed terrorist group today kidnapped a number of workers in the mission of the International Committee of the Red Cross in Syria," the report said, using a term the government frequently uses for rebels trying to topple President Bashar al-Assad.
Watson was not able to confirm that shots had been fired, but said the team's vehicles were also missing. The team had been on their way back to Damascus after delivering medical supplies in Sarmin and Idlib, he said.
Kidnappings have become increasingly common in northern Syria, where rebels have captured swathes of territory but government forces have clung on to many urban centres and fighting continues daily.
The 2-1/2-year conflict has claimed more than 100,000 lives and driven more than 2.1 million refugees out of their shattered homeland.