A firefighter required hospital treatment after being sprayed in the face while trying to stop youngsters tampering with a fire engine.
A number of fire crews have come under attack in Strathclyde
The incident happened as a crew tackled a blaze in Saltcoats, North Ayrshire.
A senior officer condemned the "callous" attack and called on community leaders to help stamp out such behaviour.
The incident came the night after three separate attacks on fire crews in Glasgow, one involving an air gun.
The latest attack came after a crew from
Ardrossan was called to a fire on open ground in New England Road Park, Saltcoats, on Saturday night.
Three youths approached the fire engine while firefighters were extinguishing the blaze.
The firefighter was sprayed in the eyes with an unknown substance when he tried to stop one of them interfering with equipment.
He received first aid from his colleagues before being taken to hospital for treatment.
Strathclyde Fire Brigade senior divisional officer Keith Small said: "This is of particular concern as it shows a shift from anti-social
abusive attacks to more frequent acts of a physical nature, which could end up with very serious consequences.
"Every firefighter puts themselves at risk to carry out their duties saving life and protecting property.
"This risk should not be increased by a minority of individuals who carry out these callous acts.
"We condemn these attacks on firefighters carrying out their crucial role in the community and call on community leaders to assist in eliminating this trend."
The previous evening a fire crew from Cowcaddens in Glasgow came under attack from youths throwing missiles in the Maryhill area.
Later than night an appliance from Govan was damaged after being shot at on Summertown Road while travelling to a report of a rubbish fire.
The same crew came under attack 30 minutes later while attending a grass fire in Ardlaw Street.